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 $206.76   13.132%   $233.9117   $233.91   $233.90   $233.90  
  Purchase #2 $51.32   10.415%   $56.665   $56.67   $56.65   $56.70  
  Purchase #3 $102.55   8.213%   $110.9724   $110.97   $110.95   $111.00  
  Purchase #4 $58.59   5.814%   $61.9964   $62.00   $62.00   $62.00  
  Purchase #5 $173.68   5.530%   $183.2845   $183.28   $183.30   $183.30  
  Purchase #6 $176.70   5.562%   $186.5281   $186.53   $186.55   $186.50  
  Purchase #7 $173.87   6.154%   $184.57   $184.57   $184.55   $184.60  
  7 purchase totals = $943.47       $1,017.9281   $1,017.93   $1,017.90   $1,018.00