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 $119.45   12.817%   $134.7599   $134.76   $134.75   $134.80  
  Purchase #2 $41.44   8.171%   $44.8261   $44.83   $44.85   $44.80  
  Purchase #3 $126.62   11.406%   $141.0623   $141.06   $141.05   $141.10  
  Purchase #4 $158.69   9.578%   $173.8893   $173.89   $173.90   $173.90  
  Purchase #5 $232.81   8.111%   $251.6932   $251.69   $251.70   $251.70  
  Purchase #6 $145.76   13.589%   $165.5673   $165.57   $165.55   $165.60  
  Purchase #7 $244.71   5.360%   $257.8265   $257.83   $257.85   $257.80  
  7 purchase totals = $1,069.48       $1,169.6246   $1,169.63   $1,169.65   $1,169.70