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 $206.64   9.485%   $226.2398   $226.24   $226.25   $226.20  
  Purchase #2 $142.89   8.144%   $154.527   $154.53   $154.55   $154.50  
  Purchase #3 $64.61   4.312%   $67.396   $67.40   $67.40   $67.40  
  Purchase #4 $247.71   11.292%   $275.6814   $275.68   $275.70   $275.70  
  Purchase #5 $15.61   5.557%   $16.4774   $16.48   $16.50   $16.50  
  Purchase #6 $60.25   7.380%   $64.6965   $64.70   $64.70   $64.70  
  Purchase #7 $234.98   9.593%   $257.5216   $257.52   $257.50   $257.50  
  7 purchase totals = $972.69       $1,062.5397   $1,062.55   $1,062.60   $1,062.50