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 $33.62   9.150%   $36.6962   $36.70   $36.70   $36.70  
  Purchase #2 $169.56   3.711%   $175.8524   $175.85   $175.85   $175.90  
  Purchase #3 $228.38   3.722%   $236.8803   $236.88   $236.90   $236.90  
  Purchase #4 $73.44   4.292%   $76.592   $76.59   $76.60   $76.60  
  Purchase #5 $120.63   11.336%   $134.3046   $134.30   $134.30   $134.30  
  Purchase #6 $118.51   11.808%   $132.5037   $132.50   $132.50   $132.50  
  Purchase #7 $250.32   11.629%   $279.4297   $279.43   $279.45   $279.40  
  7 purchase totals = $994.46       $1,072.2589   $1,072.25   $1,072.30   $1,072.30