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 $246.49   10.768%   $273.032   $273.03   $273.05   $273.00  
  Purchase #2 $157.76   7.689%   $169.8902   $169.89   $169.90   $169.90  
  Purchase #3 $197.65   7.361%   $212.199   $212.20   $212.20   $212.20  
  Purchase #4 $60.58   10.317%   $66.83   $66.83   $66.85   $66.80  
  Purchase #5 $38.66   10.807%   $42.838   $42.84   $42.85   $42.80  
  Purchase #6 $107.79   13.522%   $122.3654   $122.37   $122.35   $122.40  
  Purchase #7 $132.78   6.270%   $141.1053   $141.11   $141.10   $141.10  
  7 purchase totals = $941.71       $1,028.2599   $1,028.27   $1,028.30   $1,028.20