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 $98.39   5.736%   $104.0337   $104.03   $104.05   $104.00  
  Purchase #2 $131.93   7.413%   $141.71   $141.71   $141.70   $141.70  
  Purchase #3 $88.88   11.308%   $98.9306   $98.93   $98.95   $98.90  
  Purchase #4 $71.49   4.166%   $74.4683   $74.47   $74.45   $74.50  
  Purchase #5 $43.41   9.630%   $47.5904   $47.59   $47.60   $47.60  
  Purchase #6 $232.96   4.730%   $243.979   $243.98   $244.00   $244.00  
  Purchase #7 $72.97   4.708%   $76.4054   $76.41   $76.40   $76.40  
  7 purchase totals = $740.03       $787.1174   $787.12   $787.15   $787.10