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 $135.33   4.266%   $141.1032   $141.10   $141.10   $141.10  
  Purchase #2 $193.36   6.522%   $205.9709   $205.97   $205.95   $206.00  
  Purchase #3 $66.62   6.832%   $71.1715   $71.17   $71.15   $71.20  
  Purchase #4 $80.80   5.156%   $84.966   $84.97   $84.95   $85.00  
  Purchase #5 $93.29   10.414%   $103.0052   $103.01   $103.00   $103.00  
  Purchase #6 $159.28   10.194%   $175.517   $175.52   $175.50   $175.50  
  Purchase #7 $41.43   5.762%   $43.8172   $43.82   $43.80   $43.80  
  7 purchase totals = $770.11       $825.5510   $825.56   $825.45   $825.60