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 $57.52   8.206%   $62.2401   $62.24   $62.25   $62.20  
  Purchase #2 $67.83   10.664%   $75.0634   $75.06   $75.05   $75.10  
  Purchase #3 $25.96   8.759%   $28.2338   $28.23   $28.25   $28.20  
  Purchase #4 $100.70   10.822%   $111.5978   $111.60   $111.60   $111.60  
  Purchase #5 $198.57   12.801%   $223.9889   $223.99   $224.00   $224.00  
  Purchase #6 $245.25   11.411%   $273.2355   $273.24   $273.25   $273.20  
  Purchase #7 $105.77   11.687%   $118.1313   $118.13   $118.15   $118.10  
  7 purchase totals = $801.60       $892.4908   $892.49   $892.55   $892.40