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 $88.80   10.766%   $98.3602   $98.36   $98.35   $98.40  
  Purchase #2 $104.34   13.135%   $118.0451   $118.05   $118.05   $118.00  
  Purchase #3 $59.41   13.565%   $67.469   $67.47   $67.45   $67.50  
  Purchase #4 $249.79   9.391%   $273.2478   $273.25   $273.25   $273.20  
  Purchase #5 $29.28   8.774%   $31.849   $31.85   $31.85   $31.80  
  Purchase #6 $219.80   6.530%   $234.1529   $234.15   $234.15   $234.20  
  Purchase #7 $41.89   11.609%   $46.753   $46.75   $46.75   $46.80  
  7 purchase totals = $793.31       $869.8770   $869.88   $869.85   $869.90