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 $52.37   6.102%   $55.5656   $55.57   $55.55   $55.60  
  Purchase #2 $185.88   8.209%   $201.1389   $201.14   $201.15   $201.10  
  Purchase #3 $42.34   13.406%   $48.0161   $48.02   $48.00   $48.00  
  Purchase #4 $236.95   7.380%   $254.4369   $254.44   $254.45   $254.40  
  Purchase #5 $70.94   11.139%   $78.842   $78.84   $78.85   $78.80  
  Purchase #6 $241.37   5.439%   $254.4981   $254.50   $254.50   $254.50  
  Purchase #7 $132.35   8.339%   $143.3867   $143.39   $143.40   $143.40  
  7 purchase totals = $962.20       $1,035.8843   $1,035.90   $1,035.90   $1,035.80