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 $52.64   8.254%   $56.9849   $56.98   $57.00   $57.00  
  Purchase #2 $203.41   12.380%   $228.5922   $228.59   $228.60   $228.60  
  Purchase #3 $16.28   5.268%   $17.1376   $17.14   $17.15   $17.10  
  Purchase #4 $187.39   6.424%   $199.4279   $199.43   $199.45   $199.40  
  Purchase #5 $157.99   6.281%   $167.9134   $167.91   $167.90   $167.90  
  Purchase #6 $141.29   3.663%   $146.4655   $146.47   $146.45   $146.50  
  Purchase #7 $207.88   4.462%   $217.1556   $217.16   $217.15   $217.20  
  7 purchase totals = $966.88       $1,033.6771   $1,033.68   $1,033.70   $1,033.70