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 $67.33   12.115%   $75.487   $75.49   $75.50   $75.50  
  Purchase #2 $175.92   12.238%   $197.4491   $197.45   $197.45   $197.40  
  Purchase #3 $34.54   10.601%   $38.2016   $38.20   $38.20   $38.20  
  Purchase #4 $216.87   13.639%   $246.4489   $246.45   $246.45   $246.40  
  Purchase #5 $132.48   11.673%   $147.9444   $147.94   $147.95   $147.90  
  Purchase #6 $166.65   10.624%   $184.3549   $184.35   $184.35   $184.40  
  Purchase #7 $121.69   3.273%   $125.6729   $125.67   $125.65   $125.70  
  7 purchase totals = $915.48       $1,015.5588   $1,015.55   $1,015.55   $1,015.50