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 $203.53   13.524%   $231.0554   $231.06   $231.05   $231.10  
  Purchase #2 $142.97   4.655%   $149.6253   $149.63   $149.65   $149.60  
  Purchase #3 $37.90   4.496%   $39.604   $39.60   $39.60   $39.60  
  Purchase #4 $220.97   3.728%   $229.2078   $229.21   $229.20   $229.20  
  Purchase #5 $229.97   5.247%   $242.0365   $242.04   $242.05   $242.00  
  Purchase #6 $31.97   6.865%   $34.1647   $34.16   $34.15   $34.20  
  Purchase #7 $11.36   5.299%   $11.962   $11.96   $11.95   $12.00  
  7 purchase totals = $878.67       $937.6557   $937.66   $937.65   $937.70