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 $88.90   9.176%   $97.0575   $97.06   $97.05   $97.10  
  Purchase #2 $234.26   12.288%   $263.0459   $263.05   $263.05   $263.00  
  Purchase #3 $130.77   11.396%   $145.6725   $145.67   $145.65   $145.70  
  Purchase #4 $13.70   11.774%   $15.313   $15.31   $15.30   $15.30  
  Purchase #5 $41.80   9.286%   $45.6815   $45.68   $45.70   $45.70  
  Purchase #6 $194.50   4.662%   $203.5676   $203.57   $203.55   $203.60  
  Purchase #7 $169.39   13.776%   $192.7252   $192.73   $192.75   $192.70  
  7 purchase totals = $873.32       $963.0632   $963.07   $963.05   $963.10