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 $87.63   5.417%   $92.3769   $92.38   $92.40   $92.40  
  Purchase #2 $90.84   3.262%   $93.8032   $93.80   $93.80   $93.80  
  Purchase #3 $107.35   10.788%   $118.9309   $118.93   $118.95   $118.90  
  Purchase #4 $22.67   13.629%   $25.7597   $25.76   $25.75   $25.80  
  Purchase #5 $141.28   13.310%   $160.0844   $160.08   $160.10   $160.10  
  Purchase #6 $150.87   8.745%   $164.0636   $164.06   $164.05   $164.10  
  Purchase #7 $93.76   6.482%   $99.8375   $99.84   $99.85   $99.80  
  7 purchase totals = $694.40       $754.8562   $754.85   $754.90   $754.90