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 $56.40   11.767%   $63.0366   $63.04   $63.05   $63.00  
  Purchase #2 $123.64   13.305%   $140.0903   $140.09   $140.10   $140.10  
  Purchase #3 $183.67   6.203%   $195.0631   $195.06   $195.05   $195.10  
  Purchase #4 $82.83   7.829%   $89.3148   $89.31   $89.30   $89.30  
  Purchase #5 $231.68   4.473%   $242.043   $242.04   $242.05   $242.00  
  Purchase #6 $239.85   6.209%   $254.7423   $254.74   $254.75   $254.70  
  Purchase #7 $63.41   10.524%   $70.0833   $70.08   $70.10   $70.10  
  7 purchase totals = $981.48       $1,054.3734   $1,054.36   $1,054.40   $1,054.30