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 $74.95   12.335%   $84.1951   $84.20   $84.20   $84.20  
  Purchase #2 $23.28   7.132%   $24.9403   $24.94   $24.95   $24.90  
  Purchase #3 $241.51   5.337%   $254.3994   $254.40   $254.40   $254.40  
  Purchase #4 $223.62   7.642%   $240.709   $240.71   $240.70   $240.70  
  Purchase #5 $54.48   13.211%   $61.6774   $61.68   $61.70   $61.70  
  Purchase #6 $250.58   11.815%   $280.186   $280.19   $280.20   $280.20  
  Purchase #7 $190.54   4.265%   $198.6665   $198.67   $198.65   $198.70  
  7 purchase totals = $1,058.96       $1,144.7737   $1,144.79   $1,144.80   $1,144.80