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 $118.50   3.396%   $122.5243   $122.52   $122.50   $122.50  
  Purchase #2 $167.38   5.275%   $176.2093   $176.21   $176.20   $176.20  
  Purchase #3 $138.95   11.432%   $154.8348   $154.83   $154.85   $154.80  
  Purchase #4 $170.50   8.492%   $184.9789   $184.98   $185.00   $185.00  
  Purchase #5 $67.72   6.394%   $72.05   $72.05   $72.05   $72.10  
  Purchase #6 $93.81   12.520%   $105.555   $105.56   $105.55   $105.60  
  Purchase #7 $99.47   13.432%   $112.8308   $112.83   $112.85   $112.80  
  7 purchase totals = $856.33       $928.9831   $928.98   $929.00   $929.00