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 $56.30   11.176%   $62.5921   $62.59   $62.60   $62.60  
  Purchase #2 $234.74   5.309%   $247.2023   $247.20   $247.20   $247.20  
  Purchase #3 $236.55   13.301%   $268.0135   $268.01   $268.00   $268.00  
  Purchase #4 $12.29   12.689%   $13.8495   $13.85   $13.85   $13.80  
  Purchase #5 $57.90   9.133%   $63.188   $63.19   $63.20   $63.20  
  Purchase #6 $24.90   3.656%   $25.8103   $25.81   $25.80   $25.80  
  Purchase #7 $129.37   9.858%   $142.1233   $142.12   $142.10   $142.10  
  7 purchase totals = $752.05       $822.7790   $822.77   $822.75   $822.70