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 $217.96   11.524%   $243.0777   $243.08   $243.10   $243.10  
  Purchase #2 $63.33   9.704%   $69.4755   $69.48   $69.50   $69.50  
  Purchase #3 $164.32   11.159%   $182.6565   $182.66   $182.65   $182.70  
  Purchase #4 $209.85   3.744%   $217.7068   $217.71   $217.70   $217.70  
  Purchase #5 $202.84   12.726%   $228.6534   $228.65   $228.65   $228.70  
  Purchase #6 $178.60   5.236%   $187.9515   $187.95   $187.95   $188.00  
  Purchase #7 $130.92   4.871%   $137.2971   $137.30   $137.30   $137.30  
  7 purchase totals = $1,167.82       $1,266.8185   $1,266.83   $1,266.85   $1,267.00