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 $61.94   6.863%   $66.1909   $66.19   $66.20   $66.20  
  Purchase #2 $134.35   6.121%   $142.5736   $142.57   $142.55   $142.60  
  Purchase #3 $107.81   10.156%   $118.7592   $118.76   $118.75   $118.80  
  Purchase #4 $221.67   7.234%   $237.7056   $237.71   $237.70   $237.70  
  Purchase #5 $58.28   13.493%   $66.1437   $66.14   $66.15   $66.10  
  Purchase #6 $62.40   11.433%   $69.5342   $69.53   $69.55   $69.50  
  Purchase #7 $167.40   5.377%   $176.4011   $176.40   $176.40   $176.40  
  7 purchase totals = $813.85       $877.3083   $877.30   $877.30   $877.30