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 $218.30   7.166%   $233.9434   $233.94   $233.95   $233.90  
  Purchase #2 $178.86   12.764%   $201.6897   $201.69   $201.70   $201.70  
  Purchase #3 $117.45   7.325%   $126.0532   $126.05   $126.05   $126.10  
  Purchase #4 $124.64   13.119%   $140.9915   $140.99   $141.00   $141.00  
  Purchase #5 $187.66   7.553%   $201.834   $201.83   $201.85   $201.80  
  Purchase #6 $154.82   3.222%   $159.8083   $159.81   $159.80   $159.80  
  Purchase #7 $37.43   5.402%   $39.452   $39.45   $39.45   $39.50  
  7 purchase totals = $1,019.16       $1,103.7721   $1,103.76   $1,103.80   $1,103.80