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 $188.67   9.319%   $206.2522   $206.25   $206.25   $206.30  
  Purchase #2 $244.41   13.264%   $276.8285   $276.83   $276.85   $276.80  
  Purchase #3 $201.31   10.612%   $222.673   $222.67   $222.65   $222.70  
  Purchase #4 $83.25   9.789%   $91.3993   $91.40   $91.40   $91.40  
  Purchase #5 $220.71   7.715%   $237.7378   $237.74   $237.75   $237.70  
  Purchase #6 $46.30   11.207%   $51.4888   $51.49   $51.50   $51.50  
  Purchase #7 $138.95   10.299%   $153.2605   $153.26   $153.25   $153.30  
  7 purchase totals = $1,123.60       $1,239.6401   $1,239.64   $1,239.65   $1,239.70