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 $60.70   7.307%   $65.1353   $65.14   $65.15   $65.10  
  Purchase #2 $20.52   6.185%   $21.7892   $21.79   $21.80   $21.80  
  Purchase #3 $218.54   3.438%   $226.0534   $226.05   $226.05   $226.10  
  Purchase #4 $141.37   4.841%   $148.2137   $148.21   $148.20   $148.20  
  Purchase #5 $142.93   8.115%   $154.5288   $154.53   $154.55   $154.50  
  Purchase #6 $125.53   7.403%   $134.823   $134.82   $134.80   $134.80  
  Purchase #7 $10.83   5.408%   $11.4157   $11.42   $11.40   $11.40  
  7 purchase totals = $720.42       $761.9591   $761.96   $761.95   $761.90