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 $204.92   3.602%   $212.3012   $212.30   $212.30   $212.30  
  Purchase #2 $148.44   12.291%   $166.6848   $166.68   $166.70   $166.70  
  Purchase #3 $175.92   4.153%   $183.226   $183.23   $183.25   $183.20  
  Purchase #4 $43.33   12.221%   $48.6254   $48.63   $48.65   $48.60  
  Purchase #5 $11.94   4.238%   $12.446   $12.45   $12.45   $12.40  
  Purchase #6 $230.30   4.208%   $239.991   $239.99   $240.00   $240.00  
  Purchase #7 $44.79   10.592%   $49.5342   $49.53   $49.55   $49.50  
  7 purchase totals = $859.64       $912.8086   $912.81   $912.90   $912.70