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 $238.37   5.324%   $251.0608   $251.06   $251.05   $251.10  
  Purchase #2 $209.62   13.552%   $238.0277   $238.03   $238.05   $238.00  
  Purchase #3 $63.42   8.871%   $69.046   $69.05   $69.05   $69.00  
  Purchase #4 $154.92   12.582%   $174.412   $174.41   $174.40   $174.40  
  Purchase #5 $116.80   13.649%   $132.742   $132.74   $132.75   $132.70  
  Purchase #6 $58.47   12.324%   $65.6758   $65.68   $65.70   $65.70  
  Purchase #7 $83.88   10.857%   $92.9869   $92.99   $93.00   $93.00  
  7 purchase totals = $925.48       $1,023.9512   $1,023.96   $1,024.00   $1,023.90