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 $69.81   5.397%   $73.5776   $73.58   $73.60   $73.60  
  Purchase #2 $118.76   6.632%   $126.6362   $126.64   $126.65   $126.60  
  Purchase #3 $101.91   3.440%   $105.4157   $105.42   $105.40   $105.40  
  Purchase #4 $96.51   6.555%   $102.8362   $102.84   $102.85   $102.80  
  Purchase #5 $242.55   12.174%   $272.078   $272.08   $272.10   $272.10  
  Purchase #6 $48.48   13.818%   $55.179   $55.18   $55.20   $55.20  
  Purchase #7 $150.69   12.363%   $169.3198   $169.32   $169.30   $169.30  
  7 purchase totals = $828.71       $905.0425   $905.06   $905.10   $905.00