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 $196.35   6.678%   $209.4623   $209.46   $209.45   $209.50  
  Purchase #2 $118.90   13.103%   $134.4795   $134.48   $134.50   $134.50  
  Purchase #3 $187.55   6.207%   $199.1912   $199.19   $199.20   $199.20  
  Purchase #4 $149.89   6.825%   $160.12   $160.12   $160.10   $160.10  
  Purchase #5 $18.25   12.569%   $20.5438   $20.54   $20.55   $20.50  
  Purchase #6 $131.48   11.562%   $146.6817   $146.68   $146.70   $146.70  
  Purchase #7 $167.56   3.657%   $173.6877   $173.69   $173.70   $173.70  
  7 purchase totals = $969.98       $1,044.1662   $1,044.16   $1,044.20   $1,044.20