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 $231.81   6.424%   $246.7015   $246.70   $246.70   $246.70  
  Purchase #2 $90.25   3.794%   $93.6741   $93.67   $93.65   $93.70  
  Purchase #3 $58.83   11.349%   $65.5066   $65.51   $65.50   $65.50  
  Purchase #4 $231.65   9.114%   $252.7626   $252.76   $252.75   $252.80  
  Purchase #5 $153.50   8.669%   $166.8069   $166.81   $166.80   $166.80  
  Purchase #6 $120.72   4.190%   $125.7782   $125.78   $125.80   $125.80  
  Purchase #7 $81.67   3.346%   $84.4027   $84.40   $84.40   $84.40  
  7 purchase totals = $968.43       $1,035.6326   $1,035.63   $1,035.60   $1,035.70