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 $222.54   8.721%   $241.9477   $241.95   $241.95   $241.90  
  Purchase #2 $249.83   8.789%   $271.7876   $271.79   $271.80   $271.80  
  Purchase #3 $78.40   11.766%   $87.6245   $87.62   $87.60   $87.60  
  Purchase #4 $235.42   6.526%   $250.7835   $250.78   $250.80   $250.80  
  Purchase #5 $118.47   13.378%   $134.3189   $134.32   $134.30   $134.30  
  Purchase #6 $197.30   12.251%   $221.4712   $221.47   $221.45   $221.50  
  Purchase #7 $25.92   8.222%   $28.0511   $28.05   $28.05   $28.10  
  7 purchase totals = $1,127.88       $1,235.9845   $1,235.98   $1,235.95   $1,236.00