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 $165.30   11.847%   $184.8831   $184.88   $184.90   $184.90  
  Purchase #2 $154.44   5.301%   $162.6269   $162.63   $162.65   $162.60  
  Purchase #3 $30.41   12.427%   $34.1891   $34.19   $34.20   $34.20  
  Purchase #4 $237.73   5.770%   $251.447   $251.45   $251.45   $251.40  
  Purchase #5 $92.90   3.309%   $95.9741   $95.97   $95.95   $96.00  
  Purchase #6 $153.60   9.432%   $168.0876   $168.09   $168.10   $168.10  
  Purchase #7 $218.91   3.235%   $225.9917   $225.99   $226.00   $226.00  
  7 purchase totals = $1,053.29       $1,123.1995   $1,123.20   $1,123.25   $1,123.20