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 $60.58   12.572%   $68.1961   $68.20   $68.20   $68.20  
  Purchase #2 $149.51   6.635%   $159.43   $159.43   $159.45   $159.40  
  Purchase #3 $64.66   10.800%   $71.6433   $71.64   $71.65   $71.60  
  Purchase #4 $14.66   13.230%   $16.5995   $16.60   $16.60   $16.60  
  Purchase #5 $48.58   13.691%   $55.2311   $55.23   $55.25   $55.20  
  Purchase #6 $175.78   9.566%   $192.5951   $192.60   $192.60   $192.60  
  Purchase #7 $202.48   5.262%   $213.1345   $213.13   $213.15   $213.10  
  7 purchase totals = $716.25       $776.8296   $776.83   $776.90   $776.70