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 $246.71   5.463%   $260.1878   $260.19   $260.20   $260.20  
  Purchase #2 $156.75   11.844%   $175.3155   $175.32   $175.30   $175.30  
  Purchase #3 $103.53   4.674%   $108.369   $108.37   $108.35   $108.40  
  Purchase #4 $17.75   3.747%   $18.4151   $18.42   $18.40   $18.40  
  Purchase #5 $146.44   12.402%   $164.6015   $164.60   $164.60   $164.60  
  Purchase #6 $37.84   11.290%   $42.1121   $42.11   $42.10   $42.10  
  Purchase #7 $201.98   5.471%   $213.0303   $213.03   $213.05   $213.00  
  7 purchase totals = $911.00       $982.0313   $982.04   $982.00   $982.00