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 $124.84   9.156%   $136.2704   $136.27   $136.25   $136.30  
  Purchase #2 $214.43   6.153%   $227.6239   $227.62   $227.60   $227.60  
  Purchase #3 $232.61   3.619%   $241.0282   $241.03   $241.05   $241.00  
  Purchase #4 $42.33   13.661%   $48.1127   $48.11   $48.10   $48.10  
  Purchase #5 $218.69   5.206%   $230.075   $230.08   $230.10   $230.10  
  Purchase #6 $81.28   11.803%   $90.8735   $90.87   $90.85   $90.90  
  Purchase #7 $211.87   13.771%   $241.0466   $241.05   $241.05   $241.00  
  7 purchase totals = $1,126.05       $1,215.0303   $1,215.03   $1,215.00   $1,215.00