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 $188.69   12.301%   $211.9008   $211.90   $211.90   $211.90  
  Purchase #2 $70.53   9.123%   $76.9645   $76.96   $76.95   $77.00  
  Purchase #3 $69.40   13.715%   $78.9182   $78.92   $78.90   $78.90  
  Purchase #4 $206.44   7.582%   $222.0923   $222.09   $222.10   $222.10  
  Purchase #5 $112.75   10.851%   $124.9845   $124.98   $125.00   $125.00  
  Purchase #6 $132.46   10.289%   $146.0888   $146.09   $146.10   $146.10  
  Purchase #7 $121.88   10.219%   $134.3349   $134.33   $134.35   $134.30  
  7 purchase totals = $902.15       $995.2840   $995.27   $995.30   $995.30