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 $143.76   12.151%   $161.2283   $161.23   $161.25   $161.20  
  Purchase #2 $175.57   13.828%   $199.8478   $199.85   $199.85   $199.80  
  Purchase #3 $231.34   4.305%   $241.2992   $241.30   $241.30   $241.30  
  Purchase #4 $68.46   10.807%   $75.8585   $75.86   $75.85   $75.90  
  Purchase #5 $145.26   5.421%   $153.1345   $153.13   $153.15   $153.10  
  Purchase #6 $232.61   9.326%   $254.3032   $254.30   $254.30   $254.30  
  Purchase #7 $21.65   13.554%   $24.5844   $24.58   $24.60   $24.60  
  7 purchase totals = $1,018.65       $1,110.2559   $1,110.25   $1,110.30   $1,110.20