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 $218.44   13.771%   $248.5214   $248.52   $248.50   $248.50  
  Purchase #2 $22.63   5.726%   $23.9258   $23.93   $23.95   $23.90  
  Purchase #3 $191.58   5.744%   $202.5844   $202.58   $202.60   $202.60  
  Purchase #4 $65.46   6.386%   $69.6403   $69.64   $69.65   $69.60  
  Purchase #5 $234.78   7.304%   $251.9283   $251.93   $251.95   $251.90  
  Purchase #6 $140.65   9.752%   $154.3662   $154.37   $154.35   $154.40  
  Purchase #7 $148.52   9.460%   $162.57   $162.57   $162.55   $162.60  
  7 purchase totals = $1,022.06       $1,113.5364   $1,113.54   $1,113.55   $1,113.50