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 $215.91   4.282%   $225.1553   $225.16   $225.15   $225.20  
  Purchase #2 $234.58   9.289%   $256.3701   $256.37   $256.35   $256.40  
  Purchase #3 $30.69   5.212%   $32.2896   $32.29   $32.30   $32.30  
  Purchase #4 $164.41   10.810%   $182.1827   $182.18   $182.20   $182.20  
  Purchase #5 $239.49   6.737%   $255.6244   $255.62   $255.60   $255.60  
  Purchase #6 $44.46   12.496%   $50.0157   $50.02   $50.00   $50.00  
  Purchase #7 $56.30   7.670%   $60.6182   $60.62   $60.60   $60.60  
  7 purchase totals = $985.84       $1,062.2560   $1,062.26   $1,062.20   $1,062.30