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 $111.67   7.394%   $119.9269   $119.93   $119.95   $119.90  
  Purchase #2 $235.73   6.198%   $250.3405   $250.34   $250.35   $250.30  
  Purchase #3 $41.29   7.662%   $44.4536   $44.45   $44.45   $44.50  
  Purchase #4 $226.85   9.500%   $248.4008   $248.40   $248.40   $248.40  
  Purchase #5 $203.29   4.543%   $212.5255   $212.53   $212.55   $212.50  
  Purchase #6 $61.30   6.791%   $65.4629   $65.46   $65.45   $65.50  
  Purchase #7 $30.26   5.598%   $31.954   $31.95   $31.95   $32.00  
  7 purchase totals = $910.39       $973.0642   $973.06   $973.10   $973.10