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 $86.42   6.412%   $91.9613   $91.96   $91.95   $92.00  
  Purchase #2 $186.33   9.146%   $203.3717   $203.37   $203.35   $203.40  
  Purchase #3 $134.47   6.570%   $143.3047   $143.30   $143.30   $143.30  
  Purchase #4 $124.50   9.522%   $136.3549   $136.35   $136.35   $136.40  
  Purchase #5 $89.49   6.430%   $95.2442   $95.24   $95.25   $95.20  
  Purchase #6 $91.28   4.435%   $95.3283   $95.33   $95.35   $95.30  
  Purchase #7 $171.86   13.485%   $195.0353   $195.04   $195.05   $195.00  
  7 purchase totals = $884.35       $960.6004   $960.59   $960.60   $960.60