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 $204.51   9.657%   $224.2595   $224.26   $224.25   $224.30  
  Purchase #2 $33.72   5.492%   $35.5719   $35.57   $35.55   $35.60  
  Purchase #3 $171.93   3.466%   $177.8891   $177.89   $177.90   $177.90  
  Purchase #4 $101.53   5.727%   $107.3446   $107.34   $107.35   $107.30  
  Purchase #5 $193.57   3.313%   $199.983   $199.98   $200.00   $200.00  
  Purchase #6 $70.73   5.559%   $74.6619   $74.66   $74.65   $74.70  
  Purchase #7 $210.97   12.616%   $237.586   $237.59   $237.60   $237.60  
  7 purchase totals = $986.96       $1,057.2960   $1,057.29   $1,057.30   $1,057.40