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 $156.75   10.606%   $173.3749   $173.37   $173.35   $173.40  
  Purchase #2 $247.68   6.560%   $263.9278   $263.93   $263.95   $263.90  
  Purchase #3 $119.88   6.147%   $127.249   $127.25   $127.25   $127.20  
  Purchase #4 $14.31   9.736%   $15.7032   $15.70   $15.70   $15.70  
  Purchase #5 $84.55   9.346%   $92.452   $92.45   $92.45   $92.50  
  Purchase #6 $74.53   6.449%   $79.3364   $79.34   $79.35   $79.30  
  Purchase #7 $44.66   10.286%   $49.2537   $49.25   $49.25   $49.30  
  7 purchase totals = $742.36       $801.2970   $801.29   $801.30   $801.30