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 $64.58   13.799%   $73.4914   $73.49   $73.50   $73.50  
  Purchase #2 $190.49   5.282%   $200.5517   $200.55   $200.55   $200.60  
  Purchase #3 $159.66   11.559%   $178.1151   $178.12   $178.10   $178.10  
  Purchase #4 $20.60   8.119%   $22.2725   $22.27   $22.25   $22.30  
  Purchase #5 $179.57   13.337%   $203.5193   $203.52   $203.50   $203.50  
  Purchase #6 $46.96   5.461%   $49.5245   $49.52   $49.50   $49.50  
  Purchase #7 $191.84   8.562%   $208.2653   $208.27   $208.25   $208.30  
  7 purchase totals = $853.70       $935.7398   $935.74   $935.65   $935.80