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 $52.88   10.673%   $58.5239   $58.52   $58.50   $58.50  
  Purchase #2 $88.67   7.849%   $95.6297   $95.63   $95.65   $95.60  
  Purchase #3 $11.48   5.109%   $12.0665   $12.07   $12.05   $12.10  
  Purchase #4 $73.40   4.473%   $76.6832   $76.68   $76.70   $76.70  
  Purchase #5 $105.69   6.270%   $112.3168   $112.32   $112.30   $112.30  
  Purchase #6 $212.77   7.684%   $229.1192   $229.12   $229.10   $229.10  
  Purchase #7 $192.96   7.106%   $206.6717   $206.67   $206.65   $206.70  
  7 purchase totals = $737.85       $791.0110   $791.01   $790.95   $791.00