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 $38.35   12.749%   $43.2392   $43.24   $43.25   $43.20  
  Purchase #2 $181.84   4.627%   $190.2537   $190.25   $190.25   $190.30  
  Purchase #3 $241.50   10.441%   $266.715   $266.72   $266.70   $266.70  
  Purchase #4 $224.91   12.592%   $253.2307   $253.23   $253.25   $253.20  
  Purchase #5 $239.45   12.515%   $269.4172   $269.42   $269.40   $269.40  
  Purchase #6 $46.55   11.534%   $51.9191   $51.92   $51.90   $51.90  
  Purchase #7 $222.52   13.226%   $251.9505   $251.95   $251.95   $252.00  
  7 purchase totals = $1,195.12       $1,326.7254   $1,326.73   $1,326.70   $1,326.70