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 $63.67   5.545%   $67.2005   $67.20   $67.20   $67.20  
  Purchase #2 $152.73   13.728%   $173.6968   $173.70   $173.70   $173.70  
  Purchase #3 $246.68   5.153%   $259.3914   $259.39   $259.40   $259.40  
  Purchase #4 $133.43   4.262%   $139.1168   $139.12   $139.10   $139.10  
  Purchase #5 $156.96   5.487%   $165.5724   $165.57   $165.55   $165.60  
  Purchase #6 $87.37   8.590%   $94.8751   $94.88   $94.90   $94.90  
  Purchase #7 $143.67   9.789%   $157.7339   $157.73   $157.75   $157.70  
  7 purchase totals = $984.51       $1,057.5869   $1,057.59   $1,057.60   $1,057.60