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 $57.47   11.110%   $63.8549   $63.85   $63.85   $63.90  
  Purchase #2 $93.38   13.714%   $106.1861   $106.19   $106.20   $106.20  
  Purchase #3 $69.36   3.500%   $71.7876   $71.79   $71.80   $71.80  
  Purchase #4 $88.27   10.103%   $97.1879   $97.19   $97.20   $97.20  
  Purchase #5 $186.35   6.373%   $198.2261   $198.23   $198.25   $198.20  
  Purchase #6 $53.60   12.425%   $60.2598   $60.26   $60.25   $60.30  
  Purchase #7 $124.86   8.615%   $135.6167   $135.62   $135.60   $135.60  
  7 purchase totals = $673.29       $733.1191   $733.13   $733.15   $733.20