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 $234.57   13.480%   $266.19   $266.19   $266.20   $266.20  
  Purchase #2 $96.60   3.272%   $99.7608   $99.76   $99.75   $99.80  
  Purchase #3 $55.73   3.127%   $57.4727   $57.47   $57.45   $57.50  
  Purchase #4 $123.70   7.153%   $132.5483   $132.55   $132.55   $132.50  
  Purchase #5 $68.94   4.379%   $71.9589   $71.96   $71.95   $72.00  
  Purchase #6 $150.84   7.111%   $161.5662   $161.57   $161.55   $161.60  
  Purchase #7 $55.31   13.444%   $62.7459   $62.75   $62.75   $62.70  
  7 purchase totals = $785.69       $852.2428   $852.25   $852.20   $852.30