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 $204.25   11.291%   $227.3119   $227.31   $227.30   $227.30  
  Purchase #2 $89.90   6.850%   $96.0582   $96.06   $96.05   $96.10  
  Purchase #3 $158.56   8.414%   $171.9012   $171.90   $171.90   $171.90  
  Purchase #4 $224.32   3.441%   $232.0389   $232.04   $232.05   $232.00  
  Purchase #5 $40.75   5.855%   $43.1359   $43.14   $43.15   $43.10  
  Purchase #6 $151.94   9.541%   $166.4366   $166.44   $166.45   $166.40  
  Purchase #7 $200.34   6.420%   $213.2018   $213.20   $213.20   $213.20  
  7 purchase totals = $1,070.06       $1,150.0845   $1,150.09   $1,150.10   $1,150.00