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 $57.39   6.831%   $61.3103   $61.31   $61.30   $61.30  
  Purchase #2 $207.39   9.376%   $226.8349   $226.83   $226.85   $226.80  
  Purchase #3 $73.86   3.789%   $76.6586   $76.66   $76.65   $76.70  
  Purchase #4 $240.68   10.620%   $266.2402   $266.24   $266.25   $266.20  
  Purchase #5 $20.26   6.355%   $21.5475   $21.55   $21.55   $21.50  
  Purchase #6 $247.81   3.867%   $257.3928   $257.39   $257.40   $257.40  
  Purchase #7 $130.58   11.804%   $145.9937   $145.99   $146.00   $146.00  
  7 purchase totals = $977.97       $1,055.9780   $1,055.97   $1,056.00   $1,055.90