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 $161.80   13.401%   $183.4828   $183.48   $183.50   $183.50  
  Purchase #2 $21.99   3.757%   $22.8162   $22.82   $22.80   $22.80  
  Purchase #3 $72.31   3.198%   $74.6225   $74.62   $74.60   $74.60  
  Purchase #4 $58.47   10.537%   $64.631   $64.63   $64.65   $64.60  
  Purchase #5 $248.79   5.814%   $263.2547   $263.25   $263.25   $263.30  
  Purchase #6 $173.43   11.640%   $193.6173   $193.62   $193.60   $193.60  
  Purchase #7 $188.30   12.597%   $212.0202   $212.02   $212.00   $212.00  
  7 purchase totals = $925.09       $1,014.4447   $1,014.44   $1,014.40   $1,014.40