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 $63.84   7.400%   $68.5642   $68.56   $68.55   $68.60  
  Purchase #2 $48.50   13.295%   $54.9481   $54.95   $54.95   $54.90  
  Purchase #3 $245.99   4.754%   $257.6844   $257.68   $257.70   $257.70  
  Purchase #4 $190.73   5.703%   $201.6073   $201.61   $201.60   $201.60  
  Purchase #5 $32.40   13.873%   $36.8949   $36.89   $36.90   $36.90  
  Purchase #6 $117.43   3.341%   $121.3533   $121.35   $121.35   $121.40  
  Purchase #7 $244.85   11.425%   $272.8241   $272.82   $272.80   $272.80  
  7 purchase totals = $943.74       $1,013.8763   $1,013.86   $1,013.85   $1,013.90