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 $58.47   4.459%   $61.0772   $61.08   $61.10   $61.10  
  Purchase #2 $95.69   11.713%   $106.8982   $106.90   $106.90   $106.90  
  Purchase #3 $104.84   3.616%   $108.631   $108.63   $108.65   $108.60  
  Purchase #4 $173.71   7.793%   $187.2472   $187.25   $187.25   $187.20  
  Purchase #5 $103.91   10.434%   $114.752   $114.75   $114.75   $114.80  
  Purchase #6 $17.43   11.794%   $19.4857   $19.49   $19.50   $19.50  
  Purchase #7 $34.96   13.658%   $39.7348   $39.73   $39.75   $39.70  
  7 purchase totals = $589.01       $637.8261   $637.83   $637.90   $637.80