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 $165.98   11.823%   $185.6038   $185.60   $185.60   $185.60  
  Purchase #2 $13.51   3.742%   $14.0155   $14.02   $14.00   $14.00  
  Purchase #3 $16.64   10.859%   $18.4469   $18.45   $18.45   $18.40  
  Purchase #4 $73.93   13.161%   $83.6599   $83.66   $83.65   $83.70  
  Purchase #5 $235.76   4.446%   $246.2419   $246.24   $246.25   $246.20  
  Purchase #6 $222.47   9.410%   $243.4044   $243.40   $243.40   $243.40  
  Purchase #7 $161.42   9.156%   $176.1996   $176.20   $176.20   $176.20  
  7 purchase totals = $889.71       $967.5720   $967.57   $967.55   $967.50