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 $175.47   13.726%   $199.555   $199.56   $199.55   $199.60  
  Purchase #2 $83.67   11.473%   $93.2695   $93.27   $93.25   $93.30  
  Purchase #3 $186.47   9.414%   $204.0243   $204.02   $204.00   $204.00  
  Purchase #4 $169.57   13.815%   $192.9961   $193.00   $193.00   $193.00  
  Purchase #5 $246.41   6.355%   $262.0694   $262.07   $262.05   $262.10  
  Purchase #6 $27.42   9.476%   $30.0183   $30.02   $30.00   $30.00  
  Purchase #7 $85.68   13.566%   $97.3033   $97.30   $97.30   $97.30  
  7 purchase totals = $974.69       $1,079.2359   $1,079.24   $1,079.15   $1,079.30