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 $206.73   8.480%   $224.2607   $224.26   $224.25   $224.30  
  Purchase #2 $92.37   7.387%   $99.1934   $99.19   $99.20   $99.20  
  Purchase #3 $54.32   12.678%   $61.2067   $61.21   $61.20   $61.20  
  Purchase #4 $141.68   5.860%   $149.9824   $149.98   $150.00   $150.00  
  Purchase #5 $142.35   9.553%   $155.9487   $155.95   $155.95   $155.90  
  Purchase #6 $137.93   6.774%   $147.2734   $147.27   $147.25   $147.30  
  Purchase #7 $133.27   6.295%   $141.6593   $141.66   $141.65   $141.70  
  7 purchase totals = $908.65       $979.5246   $979.52   $979.50   $979.60