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 $118.89   13.801%   $135.298   $135.30   $135.30   $135.30  
  Purchase #2 $172.61   8.303%   $186.9418   $186.94   $186.95   $186.90  
  Purchase #3 $162.37   8.327%   $175.8905   $175.89   $175.90   $175.90  
  Purchase #4 $91.73   6.623%   $97.8053   $97.81   $97.80   $97.80  
  Purchase #5 $151.93   3.716%   $157.5757   $157.58   $157.60   $157.60  
  Purchase #6 $59.85   12.476%   $67.3169   $67.32   $67.30   $67.30  
  Purchase #7 $143.71   12.760%   $162.0474   $162.05   $162.05   $162.00  
  7 purchase totals = $901.09       $982.8756   $982.89   $982.90   $982.80