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 $65.38   12.353%   $73.4564   $73.46   $73.45   $73.50  
  Purchase #2 $31.64   9.746%   $34.7236   $34.72   $34.70   $34.70  
  Purchase #3 $164.94   6.518%   $175.6908   $175.69   $175.70   $175.70  
  Purchase #4 $102.32   12.123%   $114.7243   $114.72   $114.70   $114.70  
  Purchase #5 $191.90   3.201%   $198.0427   $198.04   $198.05   $198.00  
  Purchase #6 $79.71   11.267%   $88.6909   $88.69   $88.70   $88.70  
  Purchase #7 $66.46   9.524%   $72.7897   $72.79   $72.80   $72.80  
  7 purchase totals = $702.35       $758.1184   $758.11   $758.10   $758.10