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 $92.84   10.744%   $102.8147   $102.81   $102.80   $102.80  
  Purchase #2 $241.41   5.196%   $253.9537   $253.95   $253.95   $254.00  
  Purchase #3 $240.96   12.847%   $271.9161   $271.92   $271.90   $271.90  
  Purchase #4 $131.41   5.206%   $138.2512   $138.25   $138.25   $138.30  
  Purchase #5 $140.54   8.652%   $152.6995   $152.70   $152.70   $152.70  
  Purchase #6 $210.34   12.618%   $236.8807   $236.88   $236.90   $236.90  
  Purchase #7 $68.57   5.307%   $72.209   $72.21   $72.20   $72.20  
  7 purchase totals = $1,126.07       $1,228.7249   $1,228.72   $1,228.70   $1,228.80