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 $211.74   7.182%   $226.9472   $226.95   $226.95   $226.90  
  Purchase #2 $105.67   12.271%   $118.6368   $118.64   $118.65   $118.60  
  Purchase #3 $246.33   10.207%   $271.4729   $271.47   $271.45   $271.50  
  Purchase #4 $66.35   12.716%   $74.7871   $74.79   $74.80   $74.80  
  Purchase #5 $250.89   13.567%   $284.9282   $284.93   $284.95   $284.90  
  Purchase #6 $118.43   7.340%   $127.1228   $127.12   $127.10   $127.10  
  Purchase #7 $148.45   6.219%   $157.6821   $157.68   $157.70   $157.70  
  7 purchase totals = $1,147.86       $1,261.5771   $1,261.58   $1,261.60   $1,261.50