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 $30.67   13.637%   $34.8525   $34.85   $34.85   $34.90  
  Purchase #2 $141.76   13.356%   $160.6935   $160.69   $160.70   $160.70  
  Purchase #3 $232.91   3.143%   $240.2304   $240.23   $240.25   $240.20  
  Purchase #4 $160.95   12.851%   $181.6337   $181.63   $181.65   $181.60  
  Purchase #5 $185.95   5.606%   $196.3744   $196.37   $196.35   $196.40  
  Purchase #6 $29.66   8.540%   $32.193   $32.19   $32.20   $32.20  
  Purchase #7 $232.61   12.144%   $260.8582   $260.86   $260.85   $260.90  
  7 purchase totals = $1,014.51       $1,106.8357   $1,106.82   $1,106.85   $1,106.90