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 $47.52   6.802%   $50.7523   $50.75   $50.75   $50.80  
  Purchase #2 $131.36   11.260%   $146.1511   $146.15   $146.15   $146.20  
  Purchase #3 $184.48   11.592%   $205.8649   $205.86   $205.85   $205.90  
  Purchase #4 $213.31   10.747%   $236.2344   $236.23   $236.25   $236.20  
  Purchase #5 $106.33   10.604%   $117.6052   $117.61   $117.60   $117.60  
  Purchase #6 $24.76   4.386%   $25.846   $25.85   $25.85   $25.80  
  Purchase #7 $216.42   10.684%   $239.5423   $239.54   $239.55   $239.50  
  7 purchase totals = $924.18       $1,021.9962   $1,021.99   $1,022.00   $1,022.00