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 $60.59   13.313%   $68.6563   $68.66   $68.65   $68.70  
  Purchase #2 $116.99   8.350%   $126.7587   $126.76   $126.75   $126.80  
  Purchase #3 $144.46   4.191%   $150.5143   $150.51   $150.50   $150.50  
  Purchase #4 $204.26   8.771%   $222.1756   $222.18   $222.20   $222.20  
  Purchase #5 $203.57   11.166%   $226.3006   $226.30   $226.30   $226.30  
  Purchase #6 $81.71   10.374%   $90.1866   $90.19   $90.20   $90.20  
  Purchase #7 $94.34   12.727%   $106.3467   $106.35   $106.35   $106.30  
  7 purchase totals = $905.92       $990.9388   $990.95   $990.95   $991.00