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 $47.34   4.571%   $49.5039   $49.50   $49.50   $49.50  
  Purchase #2 $160.26   13.278%   $181.5393   $181.54   $181.55   $181.50  
  Purchase #3 $49.98   3.381%   $51.6698   $51.67   $51.65   $51.70  
  Purchase #4 $245.25   8.194%   $265.3458   $265.35   $265.35   $265.30  
  Purchase #5 $154.69   8.512%   $167.8572   $167.86   $167.85   $167.90  
  Purchase #6 $82.67   8.514%   $89.7085   $89.71   $89.70   $89.70  
  Purchase #7 $154.65   9.642%   $169.5614   $169.56   $169.55   $169.60  
  7 purchase totals = $894.84       $975.1859   $975.19   $975.15   $975.20