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 $212.54   10.493%   $234.8418   $234.84   $234.85   $234.80  
  Purchase #2 $223.61   10.767%   $247.6861   $247.69   $247.70   $247.70  
  Purchase #3 $43.65   10.531%   $48.2468   $48.25   $48.25   $48.20  
  Purchase #4 $108.34   7.856%   $116.8512   $116.85   $116.85   $116.90  
  Purchase #5 $25.67   11.609%   $28.65   $28.65   $28.65   $28.70  
  Purchase #6 $24.38   3.226%   $25.1665   $25.17   $25.15   $25.20  
  Purchase #7 $62.30   3.630%   $64.5615   $64.56   $64.55   $64.60  
  7 purchase totals = $700.49       $766.0039   $766.01   $766.00   $766.10