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 $120.98   9.318%   $132.2529   $132.25   $132.25   $132.30  
  Purchase #2 $183.31   7.323%   $196.7338   $196.73   $196.75   $196.70  
  Purchase #3 $162.26   13.291%   $183.826   $183.83   $183.85   $183.80  
  Purchase #4 $13.29   8.725%   $14.4496   $14.45   $14.45   $14.40  
  Purchase #5 $174.40   4.282%   $181.8678   $181.87   $181.85   $181.90  
  Purchase #6 $125.67   11.788%   $140.484   $140.48   $140.50   $140.50  
  Purchase #7 $150.26   13.748%   $170.9177   $170.92   $170.90   $170.90  
  7 purchase totals = $930.17       $1,020.5318   $1,020.53   $1,020.55   $1,020.50