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 $59.44   5.672%   $62.8114   $62.81   $62.80   $62.80  
  Purchase #2 $6.63   6.398%   $7.0542   $7.05   $7.05   $7.10  
  Purchase #3 $112.89   10.515%   $124.7604   $124.76   $124.75   $124.80  
  Purchase #4 $224.74   11.728%   $251.0975   $251.10   $251.10   $251.10  
  Purchase #5 $24.50   12.497%   $27.5618   $27.56   $27.55   $27.60  
  Purchase #6 $235.29   8.815%   $256.0308   $256.03   $256.05   $256.00  
  Purchase #7 $12.67   9.540%   $13.8787   $13.88   $13.90   $13.90  
  7 purchase totals = $676.16       $743.1948   $743.19   $743.20   $743.30