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 $227.70   10.723%   $252.1163   $252.12   $252.10   $252.10  
  Purchase #2 $45.91   4.298%   $47.8832   $47.88   $47.90   $47.90  
  Purchase #3 $168.42   5.296%   $177.3395   $177.34   $177.35   $177.30  
  Purchase #4 $6.65   9.793%   $7.3012   $7.30   $7.30   $7.30  
  Purchase #5 $214.98   4.865%   $225.4388   $225.44   $225.45   $225.40  
  Purchase #6 $11.32   11.391%   $12.6095   $12.61   $12.60   $12.60  
  Purchase #7 $219.95   10.201%   $242.3871   $242.39   $242.40   $242.40  
  7 purchase totals = $894.93       $965.0756   $965.08   $965.10   $965.00