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 $190.67   8.402%   $206.6901   $206.69   $206.70   $206.70  
  Purchase #2 $234.42   7.311%   $251.5584   $251.56   $251.55   $251.60  
  Purchase #3 $230.25   3.243%   $237.717   $237.72   $237.70   $237.70  
  Purchase #4 $243.94   7.471%   $262.1648   $262.16   $262.15   $262.20  
  Purchase #5 $58.77   8.836%   $63.9629   $63.96   $63.95   $64.00  
  Purchase #6 $39.87   12.673%   $44.9227   $44.92   $44.90   $44.90  
  Purchase #7 $175.60   8.147%   $189.9061   $189.91   $189.90   $189.90  
  7 purchase totals = $1,173.52       $1,256.9220   $1,256.92   $1,256.85   $1,257.00