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 $113.49   3.119%   $117.0298   $117.03   $117.05   $117.00  
  Purchase #2 $248.35   5.681%   $262.4588   $262.46   $262.45   $262.50  
  Purchase #3 $19.95   12.451%   $22.434   $22.43   $22.45   $22.40  
  Purchase #4 $85.72   6.519%   $91.3081   $91.31   $91.30   $91.30  
  Purchase #5 $10.96   6.414%   $11.663   $11.66   $11.65   $11.70  
  Purchase #6 $30.56   9.166%   $33.3611   $33.36   $33.35   $33.40  
  Purchase #7 $237.94   3.782%   $246.9389   $246.94   $246.95   $246.90  
  7 purchase totals = $746.97       $785.1937   $785.19   $785.20   $785.20