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 $57.53   11.274%   $64.0159   $64.02   $64.00   $64.00  
  Purchase #2 $63.74   5.134%   $67.0124   $67.01   $67.00   $67.00  
  Purchase #3 $114.72   9.785%   $125.9454   $125.95   $125.95   $125.90  
  Purchase #4 $192.57   6.863%   $205.7861   $205.79   $205.80   $205.80  
  Purchase #5 $47.69   11.788%   $53.3117   $53.31   $53.30   $53.30  
  Purchase #6 $131.56   7.671%   $141.652   $141.65   $141.65   $141.70  
  Purchase #7 $12.39   13.121%   $14.0157   $14.02   $14.00   $14.00  
  7 purchase totals = $620.20       $671.7392   $671.75   $671.70   $671.70