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 $103.39   12.286%   $116.0925   $116.09   $116.10   $116.10  
  Purchase #2 $192.34   7.345%   $206.4674   $206.47   $206.45   $206.50  
  Purchase #3 $10.76   10.447%   $11.8841   $11.88   $11.90   $11.90  
  Purchase #4 $212.46   7.226%   $227.8124   $227.81   $227.80   $227.80  
  Purchase #5 $174.75   3.523%   $180.9064   $180.91   $180.90   $180.90  
  Purchase #6 $170.90   3.575%   $177.0097   $177.01   $177.00   $177.00  
  Purchase #7 $102.69   3.485%   $106.2687   $106.27   $106.25   $106.30  
  7 purchase totals = $967.29       $1,026.4412   $1,026.44   $1,026.40   $1,026.50