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 $33.73   8.575%   $36.6223   $36.62   $36.60   $36.60  
  Purchase #2 $171.79   13.419%   $194.8425   $194.84   $194.85   $194.80  
  Purchase #3 $66.75   13.119%   $75.5069   $75.51   $75.50   $75.50  
  Purchase #4 $59.33   11.754%   $66.3036   $66.30   $66.30   $66.30  
  Purchase #5 $5.56   3.615%   $5.761   $5.76   $5.75   $5.80  
  Purchase #6 $208.66   8.826%   $227.0763   $227.08   $227.10   $227.10  
  Purchase #7 $12.37   3.684%   $12.8257   $12.83   $12.85   $12.80  
  7 purchase totals = $558.19       $618.9383   $618.94   $618.95   $618.90