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 $208.51   13.127%   $235.8811   $235.88   $235.90   $235.90  
  Purchase #2 $144.26   12.581%   $162.4094   $162.41   $162.40   $162.40  
  Purchase #3 $187.75   13.771%   $213.6051   $213.61   $213.60   $213.60  
  Purchase #4 $94.62   10.424%   $104.4832   $104.48   $104.50   $104.50  
  Purchase #5 $234.62   4.726%   $245.7081   $245.71   $245.70   $245.70  
  Purchase #6 $200.42   5.788%   $212.0203   $212.02   $212.00   $212.00  
  Purchase #7 $170.93   10.159%   $188.2948   $188.29   $188.30   $188.30  
  7 purchase totals = $1,241.11       $1,362.4020   $1,362.40   $1,362.40   $1,362.40