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 $185.54   8.726%   $201.7302   $201.73   $201.75   $201.70  
  Purchase #2 $244.38   4.632%   $255.6997   $255.70   $255.70   $255.70  
  Purchase #3 $142.52   6.799%   $152.2099   $152.21   $152.20   $152.20  
  Purchase #4 $24.67   7.448%   $26.5074   $26.51   $26.50   $26.50  
  Purchase #5 $219.82   10.159%   $242.1515   $242.15   $242.15   $242.20  
  Purchase #6 $163.45   11.397%   $182.0784   $182.08   $182.10   $182.10  
  Purchase #7 $88.28   8.537%   $95.8165   $95.82   $95.80   $95.80  
  7 purchase totals = $1,068.66       $1,156.1936   $1,156.20   $1,156.20   $1,156.20