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 $239.72   11.181%   $266.5231   $266.52   $266.50   $266.50  
  Purchase #2 $51.53   12.746%   $58.098   $58.10   $58.10   $58.10  
  Purchase #3 $107.59   8.394%   $116.6211   $116.62   $116.60   $116.60  
  Purchase #4 $58.94   12.829%   $66.5014   $66.50   $66.50   $66.50  
  Purchase #5 $100.96   9.252%   $110.3008   $110.30   $110.30   $110.30  
  Purchase #6 $228.47   10.705%   $252.9277   $252.93   $252.95   $252.90  
  Purchase #7 $142.29   6.810%   $151.9799   $151.98   $152.00   $152.00  
  7 purchase totals = $929.50       $1,022.9520   $1,022.95   $1,022.95   $1,022.90