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 $201.75   12.304%   $226.5733   $226.57   $226.55   $226.60  
  Purchase #2 $219.54   4.241%   $228.8507   $228.85   $228.85   $228.90  
  Purchase #3 $114.37   7.821%   $123.3149   $123.31   $123.30   $123.30  
  Purchase #4 $6.26   5.702%   $6.6169   $6.62   $6.60   $6.60  
  Purchase #5 $219.70   9.595%   $240.7802   $240.78   $240.80   $240.80  
  Purchase #6 $105.46   8.675%   $114.6087   $114.61   $114.60   $114.60  
  Purchase #7 $22.84   5.219%   $24.032   $24.03   $24.05   $24.00  
  7 purchase totals = $889.92       $964.7767   $964.77   $964.75   $964.80