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 $146.28   11.811%   $163.5571   $163.56   $163.55   $163.60  
  Purchase #2 $218.46   12.455%   $245.6692   $245.67   $245.65   $245.70  
  Purchase #3 $167.30   8.417%   $181.3816   $181.38   $181.40   $181.40  
  Purchase #4 $92.66   5.512%   $97.7674   $97.77   $97.75   $97.80  
  Purchase #5 $116.42   8.716%   $126.5672   $126.57   $126.55   $126.60  
  Purchase #6 $187.65   4.472%   $196.0417   $196.04   $196.05   $196.00  
  Purchase #7 $84.51   13.855%   $96.2189   $96.22   $96.20   $96.20  
  7 purchase totals = $1,013.28       $1,107.2031   $1,107.21   $1,107.15   $1,107.30