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 $88.91   4.163%   $92.6113   $92.61   $92.60   $92.60  
  Purchase #2 $48.97   12.154%   $54.9218   $54.92   $54.90   $54.90  
  Purchase #3 $34.94   7.327%   $37.5001   $37.50   $37.50   $37.50  
  Purchase #4 $157.33   5.163%   $165.4529   $165.45   $165.45   $165.50  
  Purchase #5 $65.74   6.252%   $69.8501   $69.85   $69.85   $69.90  
  Purchase #6 $12.89   5.752%   $13.6314   $13.63   $13.65   $13.60  
  Purchase #7 $24.62   6.244%   $26.1573   $26.16   $26.15   $26.20  
  7 purchase totals = $433.40       $460.1249   $460.12   $460.10   $460.20