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 $24.79   7.496%   $26.6483   $26.65   $26.65   $26.60  
  Purchase #2 $197.95   13.247%   $224.1724   $224.17   $224.15   $224.20  
  Purchase #3 $148.27   10.418%   $163.7168   $163.72   $163.70   $163.70  
  Purchase #4 $55.29   11.311%   $61.5439   $61.54   $61.55   $61.50  
  Purchase #5 $169.47   13.291%   $191.9943   $191.99   $192.00   $192.00  
  Purchase #6 $166.90   10.745%   $184.8334   $184.83   $184.85   $184.80  
  Purchase #7 $244.97   4.676%   $256.4248   $256.42   $256.40   $256.40  
  7 purchase totals = $1,007.64       $1,109.3339   $1,109.32   $1,109.30   $1,109.20