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 $14.59   11.753%   $16.3048   $16.30   $16.30   $16.30  
  Purchase #2 $164.26   13.341%   $186.1739   $186.17   $186.15   $186.20  
  Purchase #3 $198.91   4.219%   $207.302   $207.30   $207.30   $207.30  
  Purchase #4 $248.38   5.628%   $262.3588   $262.36   $262.35   $262.40  
  Purchase #5 $39.47   12.131%   $44.2581   $44.26   $44.25   $44.30  
  Purchase #6 $8.62   11.385%   $9.6014   $9.60   $9.60   $9.60  
  Purchase #7 $23.98   7.717%   $25.8305   $25.83   $25.85   $25.80  
  7 purchase totals = $698.21       $751.8295   $751.82   $751.80   $751.90