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 $196.43   9.513%   $215.1164   $215.12   $215.10   $215.10  
  Purchase #2 $132.74   6.728%   $141.6707   $141.67   $141.65   $141.70  
  Purchase #3 $111.55   8.125%   $120.6134   $120.61   $120.60   $120.60  
  Purchase #4 $71.82   4.361%   $74.9521   $74.95   $74.95   $75.00  
  Purchase #5 $12.81   12.633%   $14.4283   $14.43   $14.45   $14.40  
  Purchase #6 $248.72   10.778%   $275.527   $275.53   $275.55   $275.50  
  Purchase #7 $35.35   6.610%   $37.6866   $37.69   $37.70   $37.70  
  7 purchase totals = $809.42       $879.9945   $880.00   $880.00   $880.00