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 $216.75   13.608%   $246.2453   $246.25   $246.25   $246.20  
  Purchase #2 $24.99   10.800%   $27.6889   $27.69   $27.70   $27.70  
  Purchase #3 $160.46   9.205%   $175.2303   $175.23   $175.25   $175.20  
  Purchase #4 $230.33   9.799%   $252.9   $252.90   $252.90   $252.90  
  Purchase #5 $77.75   9.694%   $85.2871   $85.29   $85.30   $85.30  
  Purchase #6 $247.46   12.726%   $278.9518   $278.95   $278.95   $279.00  
  Purchase #7 $112.87   7.743%   $121.6095   $121.61   $121.60   $121.60  
  7 purchase totals = $1,070.61       $1,187.9129   $1,187.92   $1,187.95   $1,187.90