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 $209.69   11.188%   $233.1501   $233.15   $233.15   $233.20  
  Purchase #2 $96.94   7.327%   $104.0428   $104.04   $104.05   $104.00  
  Purchase #3 $188.92   11.813%   $211.2371   $211.24   $211.25   $211.20  
  Purchase #4 $162.36   10.202%   $178.924   $178.92   $178.90   $178.90  
  Purchase #5 $175.90   12.211%   $197.3791   $197.38   $197.40   $197.40  
  Purchase #6 $157.62   7.561%   $169.5376   $169.54   $169.55   $169.50  
  Purchase #7 $243.84   6.431%   $259.5214   $259.52   $259.50   $259.50  
  7 purchase totals = $1,235.27       $1,353.7921   $1,353.79   $1,353.80   $1,353.70