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 $216.49   3.546%   $224.1667   $224.17   $224.15   $224.20  
  Purchase #2 $248.87   9.749%   $273.1323   $273.13   $273.15   $273.10  
  Purchase #3 $68.39   11.315%   $76.1283   $76.13   $76.15   $76.10  
  Purchase #4 $66.65   4.123%   $69.398   $69.40   $69.40   $69.40  
  Purchase #5 $121.57   8.438%   $131.8281   $131.83   $131.85   $131.80  
  Purchase #6 $236.37   3.670%   $245.0448   $245.04   $245.05   $245.00  
  Purchase #7 $33.80   9.381%   $36.9708   $36.97   $36.95   $37.00  
  7 purchase totals = $992.14       $1,056.6690   $1,056.67   $1,056.70   $1,056.60