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 $241.35   10.811%   $267.4423   $267.44   $267.45   $267.40  
  Purchase #2 $176.84   9.450%   $193.5514   $193.55   $193.55   $193.60  
  Purchase #3 $90.79   12.389%   $102.038   $102.04   $102.05   $102.00  
  Purchase #4 $11.84   4.199%   $12.3372   $12.34   $12.35   $12.30  
  Purchase #5 $11.31   6.108%   $12.0008   $12.00   $12.00   $12.00  
  Purchase #6 $180.59   5.612%   $190.7247   $190.72   $190.70   $190.70  
  Purchase #7 $169.83   8.268%   $183.8715   $183.87   $183.85   $183.90  
  7 purchase totals = $882.55       $961.9659   $961.96   $961.95   $961.90