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 $243.79   13.635%   $277.0308   $277.03   $277.05   $277.00  
  Purchase #2 $66.73   13.435%   $75.6952   $75.70   $75.70   $75.70  
  Purchase #3 $236.86   4.184%   $246.7702   $246.77   $246.75   $246.80  
  Purchase #4 $54.85   11.749%   $61.2943   $61.29   $61.30   $61.30  
  Purchase #5 $244.98   3.439%   $253.4049   $253.40   $253.40   $253.40  
  Purchase #6 $125.84   6.838%   $134.4449   $134.44   $134.45   $134.40  
  Purchase #7 $40.39   13.678%   $45.9145   $45.91   $45.90   $45.90  
  7 purchase totals = $1,013.44       $1,094.5548   $1,094.54   $1,094.55   $1,094.50