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 $142.83   7.826%   $154.0079   $154.01   $154.00   $154.00  
  Purchase #2 $54.51   11.697%   $60.886   $60.89   $60.90   $60.90  
  Purchase #3 $13.36   7.415%   $14.3506   $14.35   $14.35   $14.40  
  Purchase #4 $179.54   10.319%   $198.0667   $198.07   $198.05   $198.10  
  Purchase #5 $126.76   4.722%   $132.7456   $132.75   $132.75   $132.70  
  Purchase #6 $111.66   11.873%   $124.9174   $124.92   $124.90   $124.90  
  Purchase #7 $97.63   8.712%   $106.1355   $106.14   $106.15   $106.10  
  7 purchase totals = $726.29       $791.1097   $791.13   $791.10   $791.10