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 $64.91   3.487%   $67.1734   $67.17   $67.15   $67.20  
  Purchase #2 $234.78   8.465%   $254.6541   $254.65   $254.65   $254.70  
  Purchase #3 $93.66   9.584%   $102.6364   $102.64   $102.65   $102.60  
  Purchase #4 $227.76   9.267%   $248.8665   $248.87   $248.85   $248.90  
  Purchase #5 $176.76   7.576%   $190.1513   $190.15   $190.15   $190.20  
  Purchase #6 $44.55   4.165%   $46.4055   $46.41   $46.40   $46.40  
  Purchase #7 $138.28   3.279%   $142.8142   $142.81   $142.80   $142.80  
  7 purchase totals = $980.70       $1,052.7014   $1,052.70   $1,052.65   $1,052.80