Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $234.52   13.387%   $265.9152   $265.92   $265.90   $265.90  
  Purchase #2 $167.73   4.772%   $175.7341   $175.73   $175.75   $175.70  
  Purchase #3 $191.29   6.601%   $203.9171   $203.92   $203.90   $203.90  
  Purchase #4 $98.56   3.546%   $102.0549   $102.05   $102.05   $102.10  
  Purchase #5 $156.26   12.697%   $176.1003   $176.10   $176.10   $176.10  
  Purchase #6 $195.90   12.822%   $221.0183   $221.02   $221.00   $221.00  
  Purchase #7 $122.34   3.507%   $126.6305   $126.63   $126.65   $126.60  
  7 purchase totals = $1,166.60       $1,271.3704   $1,271.37   $1,271.35   $1,271.30