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 $202.48   5.862%   $214.3494   $214.35   $214.35   $214.30  
  Purchase #2 $141.57   9.147%   $154.5194   $154.52   $154.50   $154.50  
  Purchase #3 $129.47   7.770%   $139.5298   $139.53   $139.55   $139.50  
  Purchase #4 $176.38   11.798%   $197.1893   $197.19   $197.20   $197.20  
  Purchase #5 $225.63   7.731%   $243.0735   $243.07   $243.05   $243.10  
  Purchase #6 $207.81   11.822%   $232.3773   $232.38   $232.40   $232.40  
  Purchase #7 $96.80   10.384%   $106.8517   $106.85   $106.85   $106.90  
  7 purchase totals = $1,180.14       $1,287.8904   $1,287.89   $1,287.90   $1,287.90