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 $219.88   11.759%   $245.7357   $245.74   $245.75   $245.70  
  Purchase #2 $203.35   11.141%   $226.0052   $226.01   $226.00   $226.00  
  Purchase #3 $112.60   8.113%   $121.7352   $121.74   $121.75   $121.70  
  Purchase #4 $219.42   12.122%   $246.0181   $246.02   $246.00   $246.00  
  Purchase #5 $214.47   12.264%   $240.7726   $240.77   $240.75   $240.80  
  Purchase #6 $164.70   10.603%   $182.1631   $182.16   $182.15   $182.20  
  Purchase #7 $19.44   10.265%   $21.4355   $21.44   $21.45   $21.40  
  7 purchase totals = $1,153.86       $1,283.8654   $1,283.88   $1,283.85   $1,283.80