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 $129.40   12.268%   $145.2748   $145.27   $145.25   $145.30  
  Purchase #2 $57.94   9.807%   $63.6222   $63.62   $63.60   $63.60  
  Purchase #3 $180.91   7.221%   $193.9735   $193.97   $193.95   $194.00  
  Purchase #4 $69.45   9.787%   $76.2471   $76.25   $76.25   $76.20  
  Purchase #5 $228.62   3.845%   $237.4104   $237.41   $237.40   $237.40  
  Purchase #6 $177.29   9.632%   $194.3666   $194.37   $194.35   $194.40  
  Purchase #7 $118.56   10.769%   $131.3277   $131.33   $131.35   $131.30  
  7 purchase totals = $962.17       $1,042.2223   $1,042.22   $1,042.15   $1,042.20