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 $70.59   8.489%   $76.5824   $76.58   $76.60   $76.60  
  Purchase #2 $231.47   11.123%   $257.2164   $257.22   $257.20   $257.20  
  Purchase #3 $156.92   13.462%   $178.0446   $178.04   $178.05   $178.00  
  Purchase #4 $153.52   12.447%   $172.6286   $172.63   $172.65   $172.60  
  Purchase #5 $214.84   8.671%   $233.4688   $233.47   $233.45   $233.50  
  Purchase #6 $66.48   12.311%   $74.6644   $74.66   $74.65   $74.70  
  Purchase #7 $29.70   4.425%   $31.0142   $31.01   $31.00   $31.00  
  7 purchase totals = $923.52       $1,023.6194   $1,023.61   $1,023.60   $1,023.60