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 $92.74   12.665%   $104.4855   $104.49   $104.50   $104.50  
  Purchase #2 $236.52   6.277%   $251.3664   $251.37   $251.35   $251.40  
  Purchase #3 $18.67   5.476%   $19.6924   $19.69   $19.70   $19.70  
  Purchase #4 $150.97   4.309%   $157.4753   $157.48   $157.50   $157.50  
  Purchase #5 $227.55   9.207%   $248.5005   $248.50   $248.50   $248.50  
  Purchase #6 $58.88   8.476%   $63.8707   $63.87   $63.85   $63.90  
  Purchase #7 $169.79   3.449%   $175.6461   $175.65   $175.65   $175.60  
  7 purchase totals = $955.12       $1,021.0369   $1,021.05   $1,021.05   $1,021.10