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 $226.62   6.450%   $241.237   $241.24   $241.25   $241.20  
  Purchase #2 $95.41   11.312%   $106.2028   $106.20   $106.20   $106.20  
  Purchase #3 $77.79   11.721%   $86.9078   $86.91   $86.90   $86.90  
  Purchase #4 $138.49   3.440%   $143.2541   $143.25   $143.25   $143.30  
  Purchase #5 $188.46   8.727%   $204.9069   $204.91   $204.90   $204.90  
  Purchase #6 $84.94   5.186%   $89.345   $89.35   $89.35   $89.30  
  Purchase #7 $156.96   5.800%   $166.0637   $166.06   $166.05   $166.10  
  7 purchase totals = $968.67       $1,037.9173   $1,037.92   $1,037.90   $1,037.90