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 $201.75   11.775%   $225.5061   $225.51   $225.50   $225.50  
  Purchase #2 $239.38   3.176%   $246.9827   $246.98   $247.00   $247.00  
  Purchase #3 $214.35   8.774%   $233.1571   $233.16   $233.15   $233.20  
  Purchase #4 $202.52   12.457%   $227.7479   $227.75   $227.75   $227.70  
  Purchase #5 $35.61   12.589%   $40.0929   $40.09   $40.10   $40.10  
  Purchase #6 $186.50   8.261%   $201.9068   $201.91   $201.90   $201.90  
  Purchase #7 $121.42   11.684%   $135.6067   $135.61   $135.60   $135.60  
  7 purchase totals = $1,201.53       $1,311.0002   $1,311.01   $1,311.00   $1,311.00