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 $52.25   11.638%   $58.3309   $58.33   $58.35   $58.30  
  Purchase #2 $78.34   12.347%   $88.0126   $88.01   $88.00   $88.00  
  Purchase #3 $156.33   4.843%   $163.9011   $163.90   $163.90   $163.90  
  Purchase #4 $192.30   10.113%   $211.7473   $211.75   $211.75   $211.70  
  Purchase #5 $232.88   5.600%   $245.9213   $245.92   $245.90   $245.90  
  Purchase #6 $45.50   11.812%   $50.8745   $50.87   $50.85   $50.90  
  Purchase #7 $118.44   7.203%   $126.9712   $126.97   $126.95   $127.00  
  7 purchase totals = $876.04       $945.7589   $945.75   $945.70   $945.70