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 $129.74   8.352%   $140.5759   $140.58   $140.60   $140.60  
  Purchase #2 $232.85   5.134%   $244.8045   $244.80   $244.80   $244.80  
  Purchase #3 $16.76   4.423%   $17.5013   $17.50   $17.50   $17.50  
  Purchase #4 $190.79   6.793%   $203.7504   $203.75   $203.75   $203.80  
  Purchase #5 $177.87   12.817%   $200.6676   $200.67   $200.65   $200.70  
  Purchase #6 $62.30   3.772%   $64.65   $64.65   $64.65   $64.70  
  Purchase #7 $170.99   10.154%   $188.3523   $188.35   $188.35   $188.40  
  7 purchase totals = $981.30       $1,060.3020   $1,060.30   $1,060.30   $1,060.50