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 $226.27   11.642%   $252.6124   $252.61   $252.60   $252.60  
  Purchase #2 $231.85   8.619%   $251.8332   $251.83   $251.85   $251.80  
  Purchase #3 $20.44   10.618%   $22.6103   $22.61   $22.60   $22.60  
  Purchase #4 $139.65   10.759%   $154.6749   $154.67   $154.65   $154.70  
  Purchase #5 $66.96   8.172%   $72.432   $72.43   $72.45   $72.40  
  Purchase #6 $219.86   10.391%   $242.7057   $242.71   $242.70   $242.70  
  Purchase #7 $156.41   9.781%   $171.7085   $171.71   $171.70   $171.70  
  7 purchase totals = $1,061.44       $1,168.5770   $1,168.57   $1,168.55   $1,168.50