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 $33.68   3.287%   $34.7871   $34.79   $34.80   $34.80  
  Purchase #2 $174.83   4.648%   $182.9561   $182.96   $182.95   $183.00  
  Purchase #3 $225.57   8.698%   $245.1901   $245.19   $245.20   $245.20  
  Purchase #4 $185.72   6.832%   $198.4084   $198.41   $198.40   $198.40  
  Purchase #5 $188.62   11.380%   $210.085   $210.09   $210.10   $210.10  
  Purchase #6 $16.84   11.727%   $18.8148   $18.81   $18.80   $18.80  
  Purchase #7 $126.47   12.571%   $142.3685   $142.37   $142.35   $142.40  
  7 purchase totals = $951.73       $1,032.6100   $1,032.62   $1,032.60   $1,032.70