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 $169.86   8.305%   $183.9669   $183.97   $183.95   $184.00  
  Purchase #2 $135.99   13.214%   $153.9597   $153.96   $153.95   $154.00  
  Purchase #3 $137.46   3.511%   $142.2862   $142.29   $142.30   $142.30  
  Purchase #4 $237.62   10.314%   $262.1281   $262.13   $262.15   $262.10  
  Purchase #5 $212.73   7.805%   $229.3336   $229.33   $229.35   $229.30  
  Purchase #6 $219.69   12.389%   $246.9074   $246.91   $246.90   $246.90  
  Purchase #7 $208.48   11.269%   $231.9736   $231.97   $231.95   $232.00  
  7 purchase totals = $1,321.83       $1,450.5555   $1,450.56   $1,450.55   $1,450.60