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 $167.77   12.632%   $188.9627   $188.96   $188.95   $189.00  
  Purchase #2 $141.98   3.563%   $147.0387   $147.04   $147.05   $147.00  
  Purchase #3 $178.86   4.410%   $186.7477   $186.75   $186.75   $186.70  
  Purchase #4 $51.63   6.611%   $55.0433   $55.04   $55.05   $55.00  
  Purchase #5 $127.86   5.123%   $134.4103   $134.41   $134.40   $134.40  
  Purchase #6 $112.77   3.601%   $116.8308   $116.83   $116.85   $116.80  
  Purchase #7 $198.64   13.125%   $224.7115   $224.71   $224.70   $224.70  
  7 purchase totals = $979.51       $1,053.7450   $1,053.74   $1,053.75   $1,053.60