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 $80.77   4.668%   $84.5403   $84.54   $84.55   $84.50  
  Purchase #2 $169.74   11.376%   $189.0496   $189.05   $189.05   $189.00  
  Purchase #3 $185.29   4.845%   $194.2673   $194.27   $194.25   $194.30  
  Purchase #4 $147.58   11.708%   $164.8587   $164.86   $164.85   $164.90  
  Purchase #5 $94.84   8.586%   $102.983   $102.98   $103.00   $103.00  
  Purchase #6 $148.87   7.754%   $160.4134   $160.41   $160.40   $160.40  
  Purchase #7 $140.37   13.384%   $159.1571   $159.16   $159.15   $159.20  
  7 purchase totals = $967.46       $1,055.2694   $1,055.27   $1,055.25   $1,055.30