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 $189.75   7.622%   $204.2127   $204.21   $204.20   $204.20  
  Purchase #2 $194.83   6.842%   $208.1603   $208.16   $208.15   $208.20  
  Purchase #3 $44.52   13.856%   $50.6887   $50.69   $50.70   $50.70  
  Purchase #4 $87.73   6.625%   $93.5421   $93.54   $93.55   $93.50  
  Purchase #5 $167.95   9.680%   $184.2076   $184.21   $184.20   $184.20  
  Purchase #6 $72.91   9.780%   $80.0406   $80.04   $80.05   $80.00  
  Purchase #7 $151.25   7.568%   $162.6966   $162.70   $162.70   $162.70  
  7 purchase totals = $908.94       $983.5486   $983.55   $983.55   $983.50