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 $62.34   7.255%   $66.8628   $66.86   $66.85   $66.90  
  Purchase #2 $246.56   5.236%   $259.4699   $259.47   $259.45   $259.50  
  Purchase #3 $15.64   7.503%   $16.8135   $16.81   $16.80   $16.80  
  Purchase #4 $238.34   11.199%   $265.0317   $265.03   $265.05   $265.00  
  Purchase #5 $35.99   8.798%   $39.1564   $39.16   $39.15   $39.20  
  Purchase #6 $167.50   6.500%   $178.3875   $178.39   $178.40   $178.40  
  Purchase #7 $135.33   10.582%   $149.6506   $149.65   $149.65   $149.70  
  7 purchase totals = $901.70       $975.3724   $975.37   $975.35   $975.50