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 $246.94   13.829%   $281.0893   $281.09   $281.10   $281.10  
  Purchase #2 $29.38   6.544%   $31.3026   $31.30   $31.30   $31.30  
  Purchase #3 $176.61   4.503%   $184.5627   $184.56   $184.55   $184.60  
  Purchase #4 $248.57   6.569%   $264.8986   $264.90   $264.90   $264.90  
  Purchase #5 $72.58   3.614%   $75.203   $75.20   $75.20   $75.20  
  Purchase #6 $100.62   11.351%   $112.0414   $112.04   $112.05   $112.00  
  Purchase #7 $101.42   10.447%   $112.0153   $112.02   $112.00   $112.00  
  7 purchase totals = $976.12       $1,061.1129   $1,061.11   $1,061.10   $1,061.10