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 $247.25   11.746%   $276.292   $276.29   $276.30   $276.30  
  Purchase #2 $104.66   12.697%   $117.9487   $117.95   $117.95   $117.90  
  Purchase #3 $67.41   7.209%   $72.2696   $72.27   $72.25   $72.30  
  Purchase #4 $24.98   11.171%   $27.7705   $27.77   $27.75   $27.80  
  Purchase #5 $97.77   10.293%   $107.8335   $107.83   $107.85   $107.80  
  Purchase #6 $114.31   5.410%   $120.4942   $120.49   $120.50   $120.50  
  Purchase #7 $201.78   10.849%   $223.6711   $223.67   $223.65   $223.70  
  7 purchase totals = $858.16       $946.2796   $946.27   $946.25   $946.30