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 $52.28   10.717%   $57.8828   $57.88   $57.90   $57.90  
  Purchase #2 $49.29   7.102%   $52.7906   $52.79   $52.80   $52.80  
  Purchase #3 $215.81   5.417%   $227.5004   $227.50   $227.50   $227.50  
  Purchase #4 $124.69   13.573%   $141.6142   $141.61   $141.60   $141.60  
  Purchase #5 $32.75   6.357%   $34.8319   $34.83   $34.85   $34.80  
  Purchase #6 $165.49   7.756%   $178.3254   $178.33   $178.35   $178.30  
  Purchase #7 $61.59   5.205%   $64.7958   $64.80   $64.80   $64.80  
  7 purchase totals = $701.90       $757.7411   $757.74   $757.80   $757.70