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 $189.84   7.569%   $204.209   $204.21   $204.20   $204.20  
  Purchase #2 $34.95   10.329%   $38.56   $38.56   $38.55   $38.60  
  Purchase #3 $94.44   7.585%   $101.6033   $101.60   $101.60   $101.60  
  Purchase #4 $241.86   3.864%   $251.2055   $251.21   $251.20   $251.20  
  Purchase #5 $217.81   4.294%   $227.1628   $227.16   $227.15   $227.20  
  Purchase #6 $78.47   8.243%   $84.9383   $84.94   $84.95   $84.90  
  Purchase #7 $169.58   8.748%   $184.4149   $184.41   $184.40   $184.40  
  7 purchase totals = $1,026.95       $1,092.0938   $1,092.09   $1,092.05   $1,092.10