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 $218.36   9.533%   $239.1763   $239.18   $239.20   $239.20  
  Purchase #2 $18.56   5.764%   $19.6298   $19.63   $19.65   $19.60  
  Purchase #3 $42.80   9.706%   $46.9542   $46.95   $46.95   $47.00  
  Purchase #4 $157.34   10.653%   $174.1014   $174.10   $174.10   $174.10  
  Purchase #5 $238.82   6.522%   $254.3958   $254.40   $254.40   $254.40  
  Purchase #6 $80.36   10.117%   $88.49   $88.49   $88.50   $88.50  
  Purchase #7 $138.49   4.219%   $144.3329   $144.33   $144.35   $144.30  
  7 purchase totals = $894.73       $967.0804   $967.08   $967.15   $967.10