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 $69.86   4.244%   $72.8249   $72.82   $72.80   $72.80  
  Purchase #2 $130.99   11.356%   $145.8652   $145.87   $145.85   $145.90  
  Purchase #3 $45.68   6.236%   $48.5286   $48.53   $48.55   $48.50  
  Purchase #4 $242.61   9.381%   $265.3692   $265.37   $265.35   $265.40  
  Purchase #5 $89.75   7.837%   $96.7837   $96.78   $96.80   $96.80  
  Purchase #6 $171.63   13.849%   $195.399   $195.40   $195.40   $195.40  
  Purchase #7 $246.98   11.851%   $276.2496   $276.25   $276.25   $276.20  
  7 purchase totals = $997.50       $1,101.0202   $1,101.02   $1,101.00   $1,101.00