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 $184.97   8.714%   $201.0883   $201.09   $201.10   $201.10  
  Purchase #2 $69.33   9.200%   $75.7084   $75.71   $75.70   $75.70  
  Purchase #3 $72.51   8.627%   $78.7654   $78.77   $78.75   $78.80  
  Purchase #4 $230.86   13.691%   $262.467   $262.47   $262.45   $262.50  
  Purchase #5 $221.67   9.216%   $242.0991   $242.10   $242.10   $242.10  
  Purchase #6 $239.96   5.588%   $253.369   $253.37   $253.35   $253.40  
  Purchase #7 $95.79   8.746%   $104.1678   $104.17   $104.15   $104.20  
  7 purchase totals = $1,115.09       $1,217.6650   $1,217.68   $1,217.60   $1,217.80