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 $80.59   5.224%   $84.8   $84.80   $84.80   $84.80  
  Purchase #2 $130.36   13.554%   $148.029   $148.03   $148.05   $148.00  
  Purchase #3 $191.29   11.754%   $213.7742   $213.77   $213.75   $213.80  
  Purchase #4 $235.59   13.222%   $266.7397   $266.74   $266.75   $266.70  
  Purchase #5 $217.29   13.193%   $245.9571   $245.96   $245.95   $246.00  
  Purchase #6 $177.27   10.134%   $195.2345   $195.23   $195.25   $195.20  
  Purchase #7 $36.87   10.740%   $40.8298   $40.83   $40.85   $40.80  
  7 purchase totals = $1,069.26       $1,195.3643   $1,195.36   $1,195.40   $1,195.30