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 $51.28   8.232%   $55.5014   $55.50   $55.50   $55.50  
  Purchase #2 $82.72   11.843%   $92.5165   $92.52   $92.50   $92.50  
  Purchase #3 $33.76   4.483%   $35.2735   $35.27   $35.25   $35.30  
  Purchase #4 $187.26   6.239%   $198.9432   $198.94   $198.95   $198.90  
  Purchase #5 $179.46   3.632%   $185.978   $185.98   $186.00   $186.00  
  Purchase #6 $224.90   6.297%   $239.062   $239.06   $239.05   $239.10  
  Purchase #7 $25.58   9.494%   $28.0086   $28.01   $28.00   $28.00  
  7 purchase totals = $784.96       $835.2832   $835.28   $835.25   $835.30