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 $156.85   8.354%   $169.9532   $169.95   $169.95   $170.00  
  Purchase #2 $169.39   7.642%   $182.3348   $182.33   $182.35   $182.30  
  Purchase #3 $240.96   13.236%   $272.8535   $272.85   $272.85   $272.90  
  Purchase #4 $144.57   9.163%   $157.8169   $157.82   $157.80   $157.80  
  Purchase #5 $34.89   4.663%   $36.5169   $36.52   $36.50   $36.50  
  Purchase #6 $197.63   7.205%   $211.8692   $211.87   $211.85   $211.90  
  Purchase #7 $155.95   12.786%   $175.8898   $175.89   $175.90   $175.90  
  7 purchase totals = $1,100.24       $1,207.2343   $1,207.23   $1,207.20   $1,207.30