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 $57.52   10.151%   $63.3589   $63.36   $63.35   $63.40  
  Purchase #2 $82.59   5.612%   $87.225   $87.23   $87.25   $87.20  
  Purchase #3 $245.56   8.618%   $266.7224   $266.72   $266.70   $266.70  
  Purchase #4 $178.55   4.414%   $186.4312   $186.43   $186.45   $186.40  
  Purchase #5 $143.89   6.427%   $153.1378   $153.14   $153.15   $153.10  
  Purchase #6 $56.44   13.239%   $63.9121   $63.91   $63.90   $63.90  
  Purchase #7 $193.62   6.274%   $205.7677   $205.77   $205.75   $205.80  
  7 purchase totals = $958.17       $1,026.5551   $1,026.56   $1,026.55   $1,026.50