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 $180.66   10.429%   $199.501   $199.50   $199.50   $199.50  
  Purchase #2 $26.36   5.547%   $27.8222   $27.82   $27.80   $27.80  
  Purchase #3 $134.63   8.448%   $146.0035   $146.00   $146.00   $146.00  
  Purchase #4 $62.57   13.793%   $71.2003   $71.20   $71.20   $71.20  
  Purchase #5 $136.45   9.132%   $148.9106   $148.91   $148.90   $148.90  
  Purchase #6 $41.59   4.263%   $43.363   $43.36   $43.35   $43.40  
  Purchase #7 $247.33   6.419%   $263.2061   $263.21   $263.20   $263.20  
  7 purchase totals = $829.59       $900.0067   $900.00   $899.95   $900.00