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 $112.77   8.741%   $122.6272   $122.63   $122.65   $122.60  
  Purchase #2 $81.95   7.412%   $88.0241   $88.02   $88.00   $88.00  
  Purchase #3 $92.82   8.124%   $100.3607   $100.36   $100.35   $100.40  
  Purchase #4 $131.52   8.667%   $142.9188   $142.92   $142.90   $142.90  
  Purchase #5 $224.44   13.308%   $254.3085   $254.31   $254.30   $254.30  
  Purchase #6 $119.27   3.168%   $123.0485   $123.05   $123.05   $123.00  
  Purchase #7 $226.34   11.808%   $253.0662   $253.07   $253.05   $253.10  
  7 purchase totals = $989.11       $1,084.3540   $1,084.36   $1,084.30   $1,084.30