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 $52.95   11.337%   $58.9529   $58.95   $58.95   $59.00  
  Purchase #2 $110.98   6.228%   $117.8918   $117.89   $117.90   $117.90  
  Purchase #3 $144.28   11.452%   $160.8029   $160.80   $160.80   $160.80  
  Purchase #4 $204.89   8.262%   $221.818   $221.82   $221.80   $221.80  
  Purchase #5 $94.43   6.230%   $100.313   $100.31   $100.30   $100.30  
  Purchase #6 $14.52   4.697%   $15.202   $15.20   $15.20   $15.20  
  Purchase #7 $180.44   11.539%   $201.261   $201.26   $201.25   $201.30  
  7 purchase totals = $802.49       $876.2416   $876.23   $876.20   $876.30