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 $34.95   6.778%   $37.3189   $37.32   $37.30   $37.30  
  Purchase #2 $75.55   3.194%   $77.9631   $77.96   $77.95   $78.00  
  Purchase #3 $235.67   5.355%   $248.2901   $248.29   $248.30   $248.30  
  Purchase #4 $58.97   9.396%   $64.5108   $64.51   $64.50   $64.50  
  Purchase #5 $33.95   9.333%   $37.1186   $37.12   $37.10   $37.10  
  Purchase #6 $240.27   6.602%   $256.1326   $256.13   $256.15   $256.10  
  Purchase #7 $184.28   9.197%   $201.2282   $201.23   $201.25   $201.20  
  7 purchase totals = $863.64       $922.5623   $922.56   $922.55   $922.50