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 $115.76   8.333%   $125.4063   $125.41   $125.40   $125.40  
  Purchase #2 $212.98   12.644%   $239.9092   $239.91   $239.90   $239.90  
  Purchase #3 $212.48   5.224%   $223.58   $223.58   $223.60   $223.60  
  Purchase #4 $67.42   4.349%   $70.3521   $70.35   $70.35   $70.40  
  Purchase #5 $12.69   11.758%   $14.1821   $14.18   $14.20   $14.20  
  Purchase #6 $160.90   3.617%   $166.7198   $166.72   $166.70   $166.70  
  Purchase #7 $223.94   4.243%   $233.4418   $233.44   $233.45   $233.40  
  7 purchase totals = $1,006.17       $1,073.5913   $1,073.59   $1,073.60   $1,073.60