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 $32.59   4.601%   $34.0895   $34.09   $34.10   $34.10  
  Purchase #2 $140.29   9.519%   $153.6442   $153.64   $153.65   $153.60  
  Purchase #3 $102.60   5.358%   $108.0973   $108.10   $108.10   $108.10  
  Purchase #4 $58.98   9.384%   $64.5147   $64.51   $64.50   $64.50  
  Purchase #5 $224.30   12.329%   $251.9539   $251.95   $251.95   $252.00  
  Purchase #6 $99.81   3.435%   $103.2385   $103.24   $103.25   $103.20  
  Purchase #7 $33.35   12.184%   $37.4134   $37.41   $37.40   $37.40  
  7 purchase totals = $691.92       $752.9515   $752.94   $752.95   $752.90