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 $240.90   11.820%   $269.3744   $269.37   $269.35   $269.40  
  Purchase #2 $98.52   10.460%   $108.8252   $108.83   $108.85   $108.80  
  Purchase #3 $26.65   8.380%   $28.8833   $28.88   $28.90   $28.90  
  Purchase #4 $91.89   3.359%   $94.9766   $94.98   $95.00   $95.00  
  Purchase #5 $61.50   6.600%   $65.559   $65.56   $65.55   $65.60  
  Purchase #6 $72.89   5.680%   $77.0302   $77.03   $77.05   $77.00  
  Purchase #7 $157.86   7.489%   $169.6821   $169.68   $169.70   $169.70  
  7 purchase totals = $750.21       $814.3308   $814.33   $814.40   $814.40