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 $139.46   6.277%   $148.2139   $148.21   $148.20   $148.20  
  Purchase #2 $191.33   3.445%   $197.9213   $197.92   $197.90   $197.90  
  Purchase #3 $241.49   13.335%   $273.6927   $273.69   $273.70   $273.70  
  Purchase #4 $195.47   5.201%   $205.6364   $205.64   $205.65   $205.60  
  Purchase #5 $148.96   10.832%   $165.0953   $165.10   $165.10   $165.10  
  Purchase #6 $226.60   3.146%   $233.7288   $233.73   $233.75   $233.70  
  Purchase #7 $122.98   13.511%   $139.5958   $139.60   $139.60   $139.60  
  7 purchase totals = $1,266.29       $1,363.8842   $1,363.89   $1,363.90   $1,363.80