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 $219.66   12.323%   $246.7287   $246.73   $246.75   $246.70  
  Purchase #2 $34.60   3.615%   $35.8508   $35.85   $35.85   $35.90  
  Purchase #3 $188.96   4.217%   $196.9284   $196.93   $196.95   $196.90  
  Purchase #4 $240.65   9.181%   $262.7441   $262.74   $262.75   $262.70  
  Purchase #5 $123.61   9.708%   $135.6101   $135.61   $135.60   $135.60  
  Purchase #6 $186.54   12.488%   $209.8351   $209.84   $209.85   $209.80  
  Purchase #7 $216.98   11.808%   $242.601   $242.60   $242.60   $242.60  
  7 purchase totals = $1,211.00       $1,330.2982   $1,330.30   $1,330.35   $1,330.20