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 $60.40   8.869%   $65.7569   $65.76   $65.75   $65.80  
  Purchase #2 $52.41   5.366%   $55.2223   $55.22   $55.20   $55.20  
  Purchase #3 $222.65   9.161%   $243.047   $243.05   $243.05   $243.00  
  Purchase #4 $247.50   13.226%   $280.2344   $280.23   $280.25   $280.20  
  Purchase #5 $70.46   12.479%   $79.2527   $79.25   $79.25   $79.30  
  Purchase #6 $153.79   5.506%   $162.2577   $162.26   $162.25   $162.30  
  Purchase #7 $133.97   3.332%   $138.4339   $138.43   $138.45   $138.40  
  7 purchase totals = $941.18       $1,024.2049   $1,024.20   $1,024.20   $1,024.20