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 $91.68   5.786%   $96.9846   $96.98   $97.00   $97.00  
  Purchase #2 $178.75   8.218%   $193.4397   $193.44   $193.45   $193.40  
  Purchase #3 $15.69   3.650%   $16.2627   $16.26   $16.25   $16.30  
  Purchase #4 $189.33   13.321%   $214.5506   $214.55   $214.55   $214.60  
  Purchase #5 $55.31   8.782%   $60.1673   $60.17   $60.15   $60.20  
  Purchase #6 $49.80   9.765%   $54.663   $54.66   $54.65   $54.70  
  Purchase #7 $179.49   11.239%   $199.6629   $199.66   $199.65   $199.70  
  7 purchase totals = $760.05       $835.7308   $835.72   $835.70   $835.90