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 $182.67   12.772%   $206.0006   $206.00   $206.00   $206.00  
  Purchase #2 $219.57   3.580%   $227.4306   $227.43   $227.45   $227.40  
  Purchase #3 $152.91   6.559%   $162.9394   $162.94   $162.95   $162.90  
  Purchase #4 $215.61   13.200%   $244.0705   $244.07   $244.05   $244.10  
  Purchase #5 $36.64   12.590%   $41.253   $41.25   $41.25   $41.30  
  Purchase #6 $21.48   10.737%   $23.7863   $23.79   $23.80   $23.80  
  Purchase #7 $164.98   12.754%   $186.0215   $186.02   $186.00   $186.00  
  7 purchase totals = $993.86       $1,091.5019   $1,091.50   $1,091.50   $1,091.50