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 $246.66   3.496%   $255.2832   $255.28   $255.30   $255.30  
  Purchase #2 $198.55   13.532%   $225.4178   $225.42   $225.40   $225.40  
  Purchase #3 $216.37   4.655%   $226.442   $226.44   $226.45   $226.40  
  Purchase #4 $83.26   11.507%   $92.8407   $92.84   $92.85   $92.80  
  Purchase #5 $199.55   13.817%   $227.1218   $227.12   $227.10   $227.10  
  Purchase #6 $228.35   11.212%   $253.9526   $253.95   $253.95   $254.00  
  Purchase #7 $207.88   3.164%   $214.4573   $214.46   $214.45   $214.50  
  7 purchase totals = $1,380.62       $1,495.5154   $1,495.51   $1,495.50   $1,495.50