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 $188.54   4.243%   $196.5398   $196.54   $196.55   $196.50  
  Purchase #2 $29.76   12.205%   $33.3922   $33.39   $33.40   $33.40  
  Purchase #3 $70.51   7.287%   $75.6481   $75.65   $75.65   $75.60  
  Purchase #4 $216.82   12.659%   $244.2672   $244.27   $244.25   $244.30  
  Purchase #5 $206.48   13.293%   $233.9274   $233.93   $233.95   $233.90  
  Purchase #6 $201.85   12.459%   $226.9985   $227.00   $227.00   $227.00  
  Purchase #7 $197.74   4.275%   $206.1934   $206.19   $206.20   $206.20  
  7 purchase totals = $1,111.70       $1,216.9666   $1,216.97   $1,217.00   $1,216.90