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 $245.88   9.284%   $268.7075   $268.71   $268.70   $268.70  
  Purchase #2 $199.61   6.869%   $213.3212   $213.32   $213.30   $213.30  
  Purchase #3 $22.86   10.278%   $25.2096   $25.21   $25.20   $25.20  
  Purchase #4 $67.99   12.669%   $76.6037   $76.60   $76.60   $76.60  
  Purchase #5 $176.97   7.234%   $189.772   $189.77   $189.75   $189.80  
  Purchase #6 $160.55   8.487%   $174.1759   $174.18   $174.20   $174.20  
  Purchase #7 $49.56   7.864%   $53.4574   $53.46   $53.45   $53.50  
  7 purchase totals = $923.42       $1,001.2473   $1,001.25   $1,001.20   $1,001.30