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 $218.55   10.627%   $241.7753   $241.78   $241.80   $241.80  
  Purchase #2 $64.85   5.175%   $68.206   $68.21   $68.20   $68.20  
  Purchase #3 $87.49   8.467%   $94.8978   $94.90   $94.90   $94.90  
  Purchase #4 $37.82   5.384%   $39.8562   $39.86   $39.85   $39.90  
  Purchase #5 $164.63   6.456%   $175.2585   $175.26   $175.25   $175.30  
  Purchase #6 $208.85   5.553%   $220.4474   $220.45   $220.45   $220.40  
  Purchase #7 $101.90   9.188%   $111.2626   $111.26   $111.25   $111.30  
  7 purchase totals = $884.09       $951.7038   $951.72   $951.70   $951.80