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 $246.83   5.541%   $260.5069   $260.51   $260.50   $260.50  
  Purchase #2 $45.48   11.263%   $50.6024   $50.60   $50.60   $50.60  
  Purchase #3 $235.98   6.416%   $251.1205   $251.12   $251.10   $251.10  
  Purchase #4 $46.50   4.289%   $48.4944   $48.49   $48.50   $48.50  
  Purchase #5 $156.55   6.873%   $167.3097   $167.31   $167.30   $167.30  
  Purchase #6 $147.53   9.700%   $161.8404   $161.84   $161.85   $161.80  
  Purchase #7 $32.96   6.757%   $35.1871   $35.19   $35.20   $35.20  
  7 purchase totals = $911.83       $975.0614   $975.06   $975.05   $975.00