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 $184.73   13.142%   $209.0072   $209.01   $209.00   $209.00  
  Purchase #2 $92.58   13.298%   $104.8913   $104.89   $104.90   $104.90  
  Purchase #3 $84.41   11.230%   $93.8892   $93.89   $93.90   $93.90  
  Purchase #4 $43.41   3.219%   $44.8074   $44.81   $44.80   $44.80  
  Purchase #5 $208.35   12.443%   $234.275   $234.28   $234.30   $234.30  
  Purchase #6 $6.35   12.566%   $7.1479   $7.15   $7.15   $7.10  
  Purchase #7 $247.64   4.696%   $259.2692   $259.27   $259.25   $259.30  
  7 purchase totals = $867.47       $953.2872   $953.30   $953.30   $953.30