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 $88.44   13.748%   $100.5987   $100.60   $100.60   $100.60  
  Purchase #2 $199.41   6.633%   $212.6369   $212.64   $212.65   $212.60  
  Purchase #3 $15.82   4.661%   $16.5574   $16.56   $16.55   $16.60  
  Purchase #4 $210.30   10.540%   $232.4656   $232.47   $232.45   $232.50  
  Purchase #5 $89.75   5.813%   $94.9672   $94.97   $94.95   $95.00  
  Purchase #6 $187.25   3.306%   $193.4405   $193.44   $193.45   $193.40  
  Purchase #7 $126.95   5.504%   $133.9373   $133.94   $133.95   $133.90  
  7 purchase totals = $917.92       $984.6036   $984.62   $984.60   $984.60