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 $86.71   13.670%   $98.5633   $98.56   $98.55   $98.60  
  Purchase #2 $212.37   6.748%   $226.7007   $226.70   $226.70   $226.70  
  Purchase #3 $219.63   5.807%   $232.3839   $232.38   $232.40   $232.40  
  Purchase #4 $218.69   5.635%   $231.0132   $231.01   $231.00   $231.00  
  Purchase #5 $101.43   13.819%   $115.4466   $115.45   $115.45   $115.40  
  Purchase #6 $26.76   5.180%   $28.1462   $28.15   $28.15   $28.10  
  Purchase #7 $218.77   7.159%   $234.4317   $234.43   $234.45   $234.40  
  7 purchase totals = $1,084.36       $1,166.6856   $1,166.68   $1,166.70   $1,166.60