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 $44.30   10.504%   $48.9533   $48.95   $48.95   $49.00  
  Purchase #2 $114.54   9.323%   $125.2186   $125.22   $125.20   $125.20  
  Purchase #3 $66.36   12.569%   $74.7008   $74.70   $74.70   $74.70  
  Purchase #4 $205.47   3.452%   $212.5628   $212.56   $212.55   $212.60  
  Purchase #5 $63.35   11.824%   $70.8405   $70.84   $70.85   $70.80  
  Purchase #6 $217.68   9.200%   $237.7066   $237.71   $237.70   $237.70  
  Purchase #7 $128.58   9.790%   $141.168   $141.17   $141.15   $141.20  
  7 purchase totals = $840.28       $911.1506   $911.15   $911.10   $911.20