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 $241.44   5.551%   $254.8423   $254.84   $254.85   $254.80  
  Purchase #2 $50.78   5.591%   $53.6191   $53.62   $53.60   $53.60  
  Purchase #3 $86.92   9.633%   $95.293   $95.29   $95.30   $95.30  
  Purchase #4 $193.70   7.477%   $208.1829   $208.18   $208.20   $208.20  
  Purchase #5 $62.85   8.829%   $68.399   $68.40   $68.40   $68.40  
  Purchase #6 $250.27   11.195%   $278.2877   $278.29   $278.30   $278.30  
  Purchase #7 $105.73   5.764%   $111.8243   $111.82   $111.80   $111.80  
  7 purchase totals = $991.69       $1,070.4483   $1,070.44   $1,070.45   $1,070.40