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 $85.38   10.369%   $94.2331   $94.23   $94.25   $94.20  
  Purchase #2 $219.47   11.155%   $243.9519   $243.95   $243.95   $244.00  
  Purchase #3 $96.72   6.321%   $102.8337   $102.83   $102.85   $102.80  
  Purchase #4 $108.44   6.491%   $115.4788   $115.48   $115.50   $115.50  
  Purchase #5 $147.32   4.609%   $154.11   $154.11   $154.10   $154.10  
  Purchase #6 $94.33   4.712%   $98.7748   $98.77   $98.75   $98.80  
  Purchase #7 $184.97   10.431%   $204.2642   $204.26   $204.25   $204.30  
  7 purchase totals = $936.63       $1,013.6465   $1,013.63   $1,013.65   $1,013.70